Editor’s Note: This article will be updated regularly. Last updated on June 15, 2021.
The Google search algorithm is a highly sophisticated system that helps millions of people around the world find the information they’re looking for in a matter of seconds. Although each search happens in an instant, there’s actually a lot going on behind the scenes.
Google analyzes your search query, matches thousands of web pages that may hold relevant information, ranks them based on hundreds of signals, considers context such as your physical location, and then returns the results in a format that is intuitive to understand.
Every year, Google makes hundreds of updates to its core and periphery search algorithms. We’ve created a guide for the most important updates from each year since the first major update in 2000.
Page Experience Update – June – Confirmed
Google will release the long-anticipated Page Experience Update in mid-June. This is a big update that impacts how Google ranks sites based on their UX. Site owners should ensure their webpages look and behave the way they’re meant to. Additionally, this update allows non-AMP content to populate the mobile Top Stories carousel for the first time (as long as it follows Google News Policies).
June 2021 Core Update – June – Confirmed
On June 2, Google announced it was releasing the first of 2 core updates landing this summer. The two-part nature of this release is due to the amount of changes the search engine wanted to include; some portions of it weren’t ready in time for a June release, so it was divided. As a result, site owners should note that changes they may see following the first round of updates may fluctuate again with July’s release.
Product Reviews Update – April – Confirmed
To provide shoppers with the most comprehensive information about a product, Google announced its update to the way it ranks product reviews. The search engine will prioritize reviews that offer unique information, analysis and research on the product over those that simply list products or features.
Featured Snippets drop – February/March – Unconfirmed
On February 19, 2021, many websites lost previously secured Featured Snippet positions. These particularly affected YMYL sites, and single-word or otherwise very short (and competitive) queries, according to Moz. Marie Haynes reported that many whose FS disappeared during this time saw them return on March 11.
Passage-Based Ranking – February – Confirmed
Google announced a new indexing method intended to identify the most relevant information from a particular webpage for a given query, no matter where on the page it lies. In other words, this update allows Google to rank passages on a webpage, not just the full webpage as a whole. In practice, this means more helpful answers should populate Featured Snippets. This update is expected to impact 7% of searches worldwide once fully rolled out.
December 2020 Core Update – December – Confirmed
Google announced its end-of-2020 update on December 3. There are no details about how certain pages may be impacted, or clues as to what types of content might experience changes in SERP positioning. Sites that see changes may need to review the content of the pages that are impacted, and look for ways to improve them according to SEO best practices.
Google Image Search Update – November – Confirmed
On February 11, 2021, Google retroactively announced that it had made a change to Google Image Search to reduce duplicate images appearing in results. The search engine also improved filter options available in image searches to refine queries that could be ambiguous, e.g. jaguar (do you mean the car? The animal? The Jacksonville, Florida, football team?).
May 2020 Core Update – May – Confirmed
Google announced this core algorithm update on May 4. The search engine didn’t provide information about what, specifically, is included in the update, or clues as to what types of content or sites might experience fluctuations in ranking.
Featured snippet update – January – Confirmed
In an effort to declutter page 1, Google no longer allows pages that are used in a featured snippet to also own a separate organic page 1 listing. This affects 100% of search results globally, but doesn’t impact a few types of featured snippets (namely, video featured snippets, top stories and interesting finds).
BERT Update – October – Confirmed
The Bidirectional Encoder Representations from Transformers Update – BERT for short – was called one of the biggest leaps forward in the history of Search, and the biggest change in the past five years. It changed the way Google interprets queries to consider how each word in a sequence relates to all other words in a sequence. This makes it easier for Google to understand complex or conversational queries, which in turn helps SERPs present the most applicable information available.
Site Diversity Update – June – Confirmed
Google announced that this update would improve SERPS with more than two duplicate sites on page one. The goal of this algorithm tweak is to create more diverse SERPs to give readers more options. The update recognizes subdomains as part of the main domain. Branded queries aren’t likely to be impacted, however. For example, searching for Amazon will still result in a page of Amazon links.
June 2019 Core Update – June – Confirmed
In a rare occurrence, Google announced this core update a day before its release. Sites previously affected by the March 2019 Core Update and the 2018 Medic Update reported ranking fluctuations. Some experts believe the update impacted YMYL pages that do not meet E.A.T. (Expertise, Authority, Trustworthiness) quality guidelines.
March 2019 Core Update – March – Confirmed
Though Google confirmed a broad core update in early March, the company provided no details about what it changed. Some sites saw their rankings fluctuate, though not significantly. Google noted that there would be no way to “fix” pages that experienced a performance drop, because they had not been directly impacted; rather, previously under-rewarded pages were benefitting from the update.
Medic Update – August – Confirmed
This update to Google’s core algorithm had a major impact on what Google calls “Your money or your life” pages. These are pages that Google has deemed potentially harmful to a user’s happiness, health or financial stability. This update reduced the likelihood that fear-mongering health websites would appear at the top of SERPs.
Mobile Speed Boost – July – Confirmed
Google announced that it would include page speed as a ranking factor in searches conducted on mobile devices. This move was meant to encourage developers to provide faster user experiences.
Video Carousel Update – June – Confirmed
In June 2018, Google stopped showing video results as organic results. In the latest version, videos were moved to a carousel that shows three video results at a time.
Snippet Length Reduction – May – Confirmed
Less than half a year since Google increased the limit for page meta descriptions, the decision was reversed. Once again, meta descriptions are limited to between 150-160 characters.
Mobile-First Indexing – March – Confirmed
After a year and a half of experimentation, Google officially rolled out its mobile-first indexing strategy. From now on, mobile versions of webpages will be used for indexing before desktop versions. Around this time, search from mobile devices was beginning to surpass desktop traffic.
Maccabees – December – Unconfirmed
Though never officially announced, Maccabees is likely several smaller updates that were rolled out around the same time. Industry insiders noticed unusual fluctuations in web traffic, including unseasonable drops near the holidays.
Snippet Increase – November – Confirmed
Prior to this update, page meta descriptions were limited to 155 characters. Google increased the limit to 300, allowing for more in-depth content.
Featured Snippets Update – October – Unconfirmed
In October 2016, webmasters noticed a drop in featured snippets for common search terms. This update remains unconfirmed.
Google Jobs – June – Confirmed
Using data from major career websites, Google began to list job opportunities at the top of relevant SERPs.
Fred – March – Unconfirmed
This unconfirmed search engine update further thwarted spam efforts from black hat SEOs and generally improved the quality of results.
Intrusiveness Penalty Update – January – Confirmed
After announcing the update five months earlier, Google rolled out penalties for mobile sites with pop-ups and interstitials that impede the user experience.
Penguin 4.0 – September/October – Confirmed
In September 2016, Google officially rolled Penguin into its core algorithm. In doing so, Google also softened Penguin penalties, instead devaluing bad links. Throughout October, Google continued to roll back harsh Penguin penalties.
Possum – September – Unconfirmed
Though never announced by Google, this update made some significant changes to local search. For instance, businesses located outside of official city limits began to appear in SERPs. Broadly, this update made the user’s location history more important than ever. A user’s browsing history may also have some weight in how pages are ranked in results.
Mobile Update 2 – May – Confirmed
As more web traffic came from mobile devices, Google doubled down on its mobile experience. This update increased the effect of the ranking signal to push mobile-friendly sites higher in SERPs.
AdWords Update – February – Confirmed
In February 2016, Google removed AdWords content from the right-hand column and placed four ad-blocks at the top of SERPs containing commercial/shopping-oriented search queries.
RankBrain – October – Confirmed
The RankBrain algorithm added machine-learning capabilities to Google Search. At launch, RankBrain improved the relevancy of results that do not specifically include query terms. Though this update likely launched sometime in the spring of 2015, it wasn’t officially announced until October.
Quality Update – May – Confirmed
This broad update tweaked how Google’s core algorithm identified quality content. Though Google didn’t offer much insight into exactly what changed, some sites saw a significant drop in traffic.
Mobile Update – April – Confirmed
In what many SEOs called “Mobilegeddon” at the time, Google announced that mobile rankings would differ from desktop rankings. For instance, if a user was searching on mobile, the algorithm would prioritize mobile-friendly websites.
e-Commerce Update – February – Unconfirmed
Though never confirmed by Google, many webmasters noticed fluctuations in site traffic in February 2015. Many suspect that Google tweaked how its algorithm handled incorrect spellings of common brand names.
Pigeon Expansion – December – Confirmed
At the end of 2014, Googled rolled out its Pigeon update to the UK, Canada and Australia.
Continuous Penguin Updates – December – Confirmed
On Dec. 10, Google announced that it would begin to update Penguin continuously, rather than push numbered updates periodically.
DMCA Update – October – Confirmed
In another push against piracy, Google reduced the likelihood that torrent sites would appear in SERPs.
Penguin 3.0 – October – Confirmed
Google pushed a new version of Penguin in October 2014 but did not extrapolate on the changes.
“In the news” Update – October – Confirmed
Google expanded the number of sites the search engine would display in news results. It also streamlined the news box UI within SERPs.
HTTPS/SSL Update – August – Confirmed
To make security more of a priority, Google added HTTPS as a ranking signal. In other words, more secure websites would be given priority over less secure sites.
Pigeon – July – Confirmed
The Pigeon updates brought together many elements of Google’s core and local search algorithms. With this update, the search engine placed more weight on the user’s location history. This allowed for more in-depth content within the Knowledge Graph, as well as a greater understanding of synonyms.
Authorship Photo Removal – June – Confirmed
In June 2014, Google officially removed all authorship photos from SERPs.
Payday Loan 3.0 – June – Confirmed
Google became very proactive in its fight against spam, pushing another update in June 2014 that broadly targeted spammy search queries.
Panda 4.0 – May – Confirmed
Another update to Panda further protected SERPs against spammy content and shady SEO tactics. It impacted about 7.5 percent of queries.
Payday Loan 2.0 – May Confirmed
This update targeted specific spam websites and “very spammy queries” in another effort to protect users.
Authorship Update – December – Unconfirmed
For a few years, many Google results included information about the page’s author, sometimes including an author portrait next to the search result. With this update, fewer results included this information and it marked the decline of Google authorship for the foreseeable future.
Hummingbird – August – Confirmed
The major Hummingbird update improved conversational search, laying the groundwork for voice search. It also made local search more precise and increased search speed dramatically. This was Google’s biggest update since Caffeine.
In-depth Articles – August – Confirmed
In August 2013, Google created another type of news result, the “in-depth article.” These were evergreen pieces such as blog posts with more depth and less dependence on freshness.
Knowledge Graph Expansion – July – Unconfirmed
Knowledge Graph expanded to include results about companies – specifically companies with robust Google+ pages. For instance, if a user searched for “Nike,” the search engine would display a card featuring a summary of the company, the location of its headquarters and current stock price.
Payday Loan Update – June – Confirmed
This summer update addressed how Google would return results of spammy search queries. Specifically, the update went after payday loans and pornography-related results.
Penguin 2.0 – June – Confirmed
The new version of Penguin updated how spam results were detected and removed from SERPs.
Domain Crowding – May – Confirmed
With this update, Google reduced the likelihood that a single domain would dominate SERP results after page two.
Phantom – May – Unconfirmed
In May 2013, many websites reported dropping traffic levels. There was much speculation from webmasters, but no official announcement from Google.
Knowledge Graph Expansion – December – Confirmed
At the end of 2012, Google expanded the Knowledge Graph to non-English search queries.
65-Pack Update – October – Confirmed
This pack of updates was filled with small algorithm improvements, such as improved UI for movie showtimes and sports scores. It also added better handling of natural language to universal search.
Exact-Match Domains – September – Confirmed
Google devalued exact-match domains with this update. For example a search for cool bow ties would bring up the most relevant bow tie content and not just direct the user to “coolbowties.com.”
7-Result SERPS – August – Unconfirmed
For some search queries, Google began to display seven results instead of 10. Industry insiders claim this update impacted 18 percent of keywords.
86-Pack Update – August – Confirmed
This pack included all updates made in the summer of 2012. Most were small tweaks, such as a feature to show the live results of soccer games during the European championship.
DMCA Penalty – August – Confirmed
Google began to penalize webpages with repeated copyright violations.
39-Pack Update – June – Confirmed
This pack included updates to how the algorithm identified hacked pages, made additional autocomplete improvements, rolled out music-related rich snippets at the international level and improved how the algorithm detected fresh content.
Knowledge Graph – May – Confirmed
With this update, SERPs began to feature more content on the right side of the page. Related search results appeared for search queries that could mean more than one thing. The knowledge graph also included people summaries pulled from Wikipedia.
52-Pack Update – May – Confirmed
The biggest pack of updates released so far, this one included bug fixes, larger snippets, better handling of non-English languages and internationalization of the search engine’s “Did you mean…?” feature.
Penguin – April – Confirmed
Also known as the “Webspam Update,” Penguin further penalized shady SEO tactics like keyword stuffing.
Panda 3.5 – April – Confirmed
Once again, Google updated Panda but did not announce specific changes.
50-Pack Update – April – Confirmed
This large pack of updates added math symbols to autocomplete, improved handling of symbols for indexing and refreshed UI in the News tab.
Panda 3.4 – March – Confirmed
For the first time, Google announced an update on Twitter. Without elaborating, the company said that the Panda 3.4 refresh would impact 1.6 percent of searches.
Venice – February – Confirmed
With Venice, Google made search more local, offering users results that were more closely tied with their location history.
40-Pack Update – February – Confirmed
This pack of updates was filled with minor changes to the search engine’s core algorithm as well as small bug fixes. It standardized thumbnails in results, tweaked ‘related to’ searches and fine-tuned autocomplete.
Panda 3.3 – February – Confirmed
Though Google made no official statement about this update, webmasters saw growth in organic referrals as a result of tweaks to Panda.
17-Pack Update – February – Confirmed
This pack of small updates made autocomplete faster, improved spelling correction and made minor adjustments to Image Search UI.
Ads Above The Fold – January – Confirmed
In January 2012, Google began to devalue pages that were “top heavy” with ads. Google predicted the update would impact about 1 percent of searches.
Panda 3.2 – January – Confirmed
Google “refreshed” the way Panda handled data with this update. No specifics were given.
Search+Your World – January – Confirmed
With this update, Google added Social Search to its SERPs. When searching for a person the user is connected with on Google+, their profile and relevant information would appear directly in the SERP. As almost all Android users automatically had a Google+ profiles, this update impacted a substantial amount of searches.
30-Pack Update – January – Confirmed
At the beginning of 2012, Google unveiled 30 tweaks to its algorithm, including bug fixes and improved analysis of landing pages for image search. Other updates improved 404 detection, created more rich snippets, updated foreign language search and more.
10-Pack Update – December – Confirmed
Google announced 10 small algorithm updates, including more comprehensive indexing, better autocomplete functionality, signals for original content and freshness attributes to image content.
Freshness Update – November – Confirmed
With this update, Google began to reward link freshness. Essentially, new content about time-sensitive topics would be given precedence over older content. For example, if a user searches for “World Series” they’ll get results about this year’s event, not last year’s.
Query Encryption – October – Confirmed
To better protect user privacy as search engine results became more personalized, and relied more on user search history, Google implemented SSL encryption on all search queries from users with a Google account.
Panda 2.5 – September – Confirmed
Webmasters reported seeing drops in page rankings as a result of a new update to Panda. However, Google did not comment on the changes it made.
Pagination Elements – September – Confirmed
Paginated content had been at risk of being identified as duplicate content prior to this update. To combat this problem, Google introduced the rel=”next” and rel=”prev” link attributes.
Expanded Sitelinks – August – Confirmed
When users search for a specific brand or site, the result often includes links to webpages on the domain. In August 2011, Google reformatted the way these links appear, giving users a better idea of where they’re going when they click a link.
Panda 2.4 – August – Confirmed
Google extended the Panda algorithm to all non-English search queries, except those made in Chinese, Japanese and Korean.
Panda 2.3 – July – Confirmed
Google made additional tweaks to its Panda algorithm but did not provide any specifics.
Google+ – June – Confirmed
On June 28, 2011, Google launched its Facebook competitor Google+. The platform was focused on giving users the ability to share content with their friends, family and colleagues. It was integrated into Gmail at launch.
Panda 2.2 – June – Confirmed
This update improved scraper detection by the Panda algorithm.
Schema.org – June – Confirmed
In a joint announcement with Microsoft and Yahoo, Google announced Schema.org, a foundation for helping developers and site owners to learn about structured data and how to make their sites appear in SERPs. The announcement not only formalized existing types of microdata but also introduced new types.
Panda 2.1 – May – Confirmed
Google confirmed that it made slight tweaks to the Panda algorithm in May 2011 but didn’t share any details.
Panda 2 – April – Confirmed
Google extended the Panda update to all English search queries worldwide. With this new rollout, Google also included algorithm improvements to weed out low-quality websites and boost the accuracy of results.
+1 Button – March – Confirmed
In March 2011, Google added the +1 button to its search engine. Users could click this button to essentially recommend links and sites to other users. The more button presses a link received, the higher it went in SERPs.
Panda – February – Confirmed
To address complaints about thin and spammy content making its way to the front page of search results, Google introduced the Panda update. Targeting “content farms” that lured in users only to show them more ads than content, this update impacted roughly 12 percent of all search results.
Attribution Update – January – Confirmed
This update reduced the chances of spammy links appearing in Google results. For example, if a webpage was stolen and reposted to another domain, Google would be more likely to show the original copy.
Overstock.com Penalty – January – Unconfirmed
On Feb. 24, The Wall Street Journal reported that Overstock.com had been artificially boosting its SERP rankings by encouraging colleges and universities to post links to its website in exchange for student and faculty discounts. Because .edu domains carry significant authority, links from these sites sent Overstock.com to the top of SERPs. JCPenny was caught by the New York Times practicing similar tactics. Google penalized both companies.
Negative Reviews – December – Confirmed
On Nov. 26, The New York Times reported that something disturbing was happening on Google SERPs. Essentially, companies could get their sites to the top of search results by abusing their customers. For example, a company might take a customer’s money but never deliver the promised product or service. Inevitably, a flood of negative reviews would appear on the site. The Google algorithm would consider this a positive and push the website further up the rankings where more people would encounter it. From there, the cycle would continue.
Less than a week after the story broke, Google amended its algorithm to punish websites and companies that treat their customers poorly.
Social Signals – December – Unconfirmed
In addition to the traditional signals used to score page rankings such as page authority and meta tags, Google and other search engines began to incorporate social signals. Pages that were shared or “liked” frequently on social media websites gained a bump in rankings.
Instant Previews – November – Confirmed
After rolling out Google Instant, the search giant added a new visual search feature to its SERPs. Users could click on a magnifying glass icon near each SERP listing to see a preview of the webpage. This encouraged site owners to put more effort into their site design.
Google Instant – September – Confirmed
With this update, Google Suggest evolved into Google Instant, which displayed results as a query was being typed. One way Instant differed from Suggest was the inclusion of localization. For example, if a user in Boston began to search for “coffee shops,” it might predict the queries “coffee shops in Boston” or “coffee shops in Cambridge MA.”
Brand Update – August – Unconfirmed
Beginning in August 2010, Google allowed domains to appear multiple times on a SERP. Prior to this update, a domain could only appear in one or two listings.
Caffeine – June – Confirmed
Google claims that the Caffeine update provided a 50 percent increase in search speed. By more closely tying together crawling and indexing, Google’s algorithm was able to ensure that the results presented to users were as fresh as possible.
May Day – May – Confirmed
The May Day update significantly reduced the strength of long-tail traffic. Specifically, Google lowered the ranking of pages that contained keywords but were thin on content. For example, ecommerce pages that only listed a single product and a small description.
Google Places – April – Confirmed
With the April 2010 update, the Local Business Center became Google Places. Place pages were originally a part of of Maps, but soon became integrated with local search. Businesses could claim a page, fill out relevant information and include promotional elements such as coupons.
Real-time Search – December – Confirmed
In 2009, social media sites and internet-based news sources were on the rise. To give users the most up-to-date results, Google rolled out real-time search. When users submitted a query for an event or topic with time-sensitive component, they would see results arrive in real time.
Vince – February – Unconfirmed
Though called a “minor change” by Google at the time, the Vince update appeared to give big brands a leg up in search results.
Rel-Canonical Tag – February – Confirmed
In February 2009, Google, Yahoo and Microsoft jointly announced the canonical tag. This tag tells the search engine which version of a page is the master copy. It can prevent search engines from penalizing syndicated content as a duplicate.
Google Suggest – August – Confirmed
In August 2008, Google introduced the suggest feature we’re so familiar with today. When users typed a query into the Google Search bar, a dropdown menu appeared to suggest potential searches. We may take this functionality for granted today, but it was a novel idea at the time.
Dewey – April – Confirmed
Once again, webmasters noticed page ranking changes but, without any specifics from Google, were unable to pinpoint exactly what had happened. Some experts speculated that Google was further integrating its Google Books product into the search engine.
Buffy – June – Unconfirmed
According to internet lore, the Buffy update was named in honor of Google’s SEO evangelist Vanessa Fox’s departure from the company. Buffy the Vampire Slayer was Fox’s favorite TV show at the time.
Buffy represented a collection of small changes continuing the objectives of the Universal Search update.
Universal Search – May – Confirmed
Perhaps the most radical change to the Google SERP since its inception, the May 2007 update did away with the traditional 10-result page. With the new update, Google included news stories, videos, images and local content in all searches.
False Alarm – December – Unconfirmed
Once again, webmasters around the world reported seeing changes to their page rankings, but Google denied making any updates.
Supplemental Update – November – Unconfirmed
Though Google made no official announcements, there were a number of updates to the supplemental index throughout 2006. At the time, webmasters were still confused as to why some of their pages were indexed differently.
Big Daddy – December – Confirmed
This large infrastructure update launched in December 2005 and was completed by March 2006. Though it didn’t have much impact on search results, Big Daddy changed the way Google dealt with 301/302 redirects, URL canonicalization and supplemental indexes.
Google Local/Maps – October – Confirmed
In October 2005, Google merged its Maps data with its recently launched Local Business Center. This update encouraged businesses to update their information with Google to better support local searches.
Jagger – October – Confirmed
Rolled out between September and November of 2005, Jagger made changes to how Google handled low-quality links.
Gilligan – September – Unconfirmed
In September 2005, webmasters reported seeing changes to their page rankings. However, Google denied updating its algorithms. Though likely a matter of semantics over what really constitutes an update, this one remains a mystery.
XML Sitemaps – June – Confirmed
June 2005 marked the first time webmasters could submit XML sitemaps directly to Google. This gave SEO professionals some influence over how their sites were crawled.
Personalized Search – June – Confirmed
Prior to this update, Google users needed to manually adjust search engine settings to get personalized results. In June 2005, Google began to utilize user search history to automatically adjust results.
Bourbon – May – Confirmed
The Bourbon update was unofficially announced by a Webmaster forum user who posted under the screen name “GoogleGuy.” Internet detectives believe GoogleGuy was none other than Matt Cutts, an engineer who worked for Google at the time.
Bourbon made changes to how the Google algorithm handled 302 redirects and duplicate content.
Allegra – February – Unconfirmed
Though not announced by Google, webmasters noticed page ranking changes in February 2005. Industry insiders speculated that Google had tweaked its Latent Semantic Indexing rules.
Nofollow – January – Confirmed
This update was implemented by Google, Microsoft and Yahoo at the same time. The nofollow attribute was meant to clean up spam links. The rel=”nofollow” attribute could be added to any link to explicitly state the link had not been approved by the site owner.
Brandy – February – Confirmed
This search engine update introduced the concept of Latent Semantic Indexing, which gave the algorithm the ability to better understand synonyms to aid in keyword analysis. Brandy also developed the idea of “link neighborhoods” which gave more weight to how sites link to one another.
Austin – January – Unconfirmed
The Austin update continued to crack down on nefarious SEO tactics such as meta-tag stuffing and invisible text. Link farms were penalized or banned outright. Content relevancy began to carry weight in page rankings.
Florida – November – Confirmed
Many SEO experts consider Google’s Florida update to signal the beginning of the modern era of SEO. In a single sweep, many webpages were wiped from the first page of search results. Unsavory tactics like stuffing blog posts with keywords were made obsolete.
Supplemental Index – September – Unconfirmed
This update allowed Google to index more pages while maintaining performance standards. SEO experts at the time worried that pages in the supplemental index would suffer in page rankings.
Fritz – July – Confirmed
Fritz changed the way Google made updates to its algorithm. Rather than overhauling the system on a monthly basis, Fritz allowed Google to make changes daily.
Esmeralda – June – Unconfirmed
This is the last of Google’s initial monthly planned updates to its search engine. Industry insiders speculate that Esmeralda contained major changes to the infrastructure of Google’s ranking algorithms.
Dominic – May – Unconfirmed
In May 2003, webmasters noticed Google bots named Freshbot and Deepcrawler scouring their websites. It also seems that Dominic altered the way Google counted and reported backlinks.
Cassandra – April – Unconfirmed
The Cassandra update cracked down on nefarious SEO tricks such as hidden text and links. It also made it more difficult for webmasters to generate link authority from co-owned domains.
Boston – February – Confirmed
The first named Google update was announced at the annual technical meeting of the Society of Engineering Science at Northeastern University. At the time, Google planned to release monthly updates to its algorithm, but this strategy was quickly abandoned for daily updates.
1st Documented Update – September – Unconfirmed
In autumn 2002, webmasters noticed differences in the search engine’s PageRank algorithm. Rather than solving many issues, SEO insiders reported seeing more 404 pages as well as pages ranking for unrelated keywords.
Google Toolbar – December – Confirmed
In the beginning, there was the Google Toolbar, a browser plugin that showed users the importance of pages with Google’s PageRank technology. Read Google’s announcement that began all the SEO conversations that continue to this day.