Founded as an independent company in 1996, Alexa was acquired by Amazon in 1999. Its toolbar collects data on browsing behavior and transmits them to the Alexa website, where they are stored and analyzed. This is the basis for the company's web traffic reporting. According to its website, Alexa provides traffic data, global rankings, and other information on 30 million websites. As of 2015, its website has been visited by over 6.5 million people monthly.
Alexa Internet was founded in April 1996 by American web entrepreneurs Brewster Kahle and Bruce Gilliat. The company's name was chosen in homage to the Library of Alexandria of Ptolemaic Egypt, drawing a parallel between the largest repository of knowledge in the ancient world and the potential of the Internet to become a similar store of knowledge. Alexa initially offered a toolbar that gave Internet users suggestions on where to go next, based on the traffic patterns of its user community. The company also offered context for each site visited: to whom it was registered, how many pages it had, how many other sites pointed to it, and how frequently it was updated. Alexa's operations grew to include archiving of web pages as they are crawled. This database served as the basis for the creation of the Internet Archive accessible through the Wayback Machine. In 1998, the company donated a copy of the archive, two terabytes in size, to the Library of Congress.
Alexa continues to supply the Internet Archive with Web crawls. In 1999, as the company moved away from its original vision of providing an "intelligent" search engine, Alexa was acquired by Amazon.com for approximately US$250 million in Amazon stock.
Alexa began a partnership with Google in early 2002, and with the web directory DMOZ in January 2003. In May 2006, Google was replaced with Bing (at the time known as Windows Live Search) as a provider of search results.
In December 2006, Amazon released Alexa Image Search. Built in-house, it was the first major application built on the company's Web platform. In December 2005, Alexa opened its extensive search index and Web-crawling facilities to third-party programs through a comprehensive set of Web services and APIs. These could be used, for instance, to construct vertical search engines that could run on Alexa's own servers or elsewhere. In May 2007, Alexa changed their API to limit comparisons to three websites, reduce the size of embedded graphs in Flash, and add mandatory embedded BritePic advertisements.
In April 2007, the company filed a lawsuit, Alexa v. Hornbaker, to stop trademark infringement by the Statsaholic service. In the lawsuit, Alexa alleged that Ron Hornbaker was stealing traffic graphs for profit, and that the primary purpose of his site was to display graphs that were generated by Alexa's servers. Hornbaker removed the term Alexa from his service name on March 19, 2007. On November 27, 2008, Amazon announced that Alexa Web Search was no longer accepting new customers, and that the service would be deprecated or discontinued for existing customers on January 26, 2009. Thereafter, Alexa became a purely analytics-focused company.
On March 31, 2009, Alexa launched a major website redesign. The redesigned site provided new web traffic metrics—including average page views per individual user, bounce rate, and user time on site. In the following weeks, Alexa added more features, including visitor demographics, clickstream and search traffic statistics. Alexa introduced these new features to compete with other web analytics services.
Alexa ranks sites based primarily on tracking a sample set of Internet traffic—users of its toolbar for the Internet Explorer, Firefox and Google Chrome web browsers. The Alexa Toolbar includes a popup blocker, a search box, links to Amazon.com and the Alexa homepage, and the Alexa ranking of the site that the user is visiting. It also allows the user to rate the site and view links to external, relevant sites. In early 2005, Alexa stated that there had been 10 million downloads of the toolbar, though the company did not provide statistics about active usage. Originally, web pages were only ranked amongst users who had the Alexa Toolbar installed, and could be biased if a specific audience subgroup was reluctant to take part in the rankings. This caused some controversies over how representative Alexa's user base was of typical Internet behavior, especially for less-visited sites. In 2007, Michael Arrington provided examples of Alexa rankings known to contradict data from the comScore web analytics service, including ranking YouTube ahead of Google.
Until 2007, a third-party-supplied plugin for the Firefox browser served as the only option for Firefox users after Amazon abandoned its A9 toolbar. On July 16, 2007, Alexa released an official toolbar for Firefox called Sparky. On 16 April 2008, many users reported drastic shifts in their Alexa rankings. Alexa confirmed this later in the day with an announcement that they had released an updated ranking system, claiming that they would now take into account more sources of data "beyond Alexa Toolbar users".
A number of antivirus companies have assessed Alexa's toolbar. The toolbar for Internet Explorer 7 was at one point flagged as malware by Microsoft Defender. Symantec classifies the toolbar as "trackware", while McAfee classifies it as adware, deeming it a "potentially unwanted program." McAfee Site Advisor rates the Alexa site as "green", finding "no significant problems" but warning of a "small fraction of downloads ... that some people consider adware or other potentially unwanted programs." Though it is possible to delete a paid subscription within an Alexa account, it is not possible to delete an account that is created at Alexa through any web interface, though any user may contact the company via its support webpage.
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