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The like button on the social networking website Facebook was first enabled on February 9, 2009. The like button enables users to easily interact with status updates, comments, photos and videos, links shared by friends, and advertisements. Once clicked by a user, the designated content appears in the News Feeds of that user's friends, and the button also displays the number of other users who have liked the content, including a full or partial list of those users. The like button was extended to comments in June 2010. After extensive testing and years of questions from the public about whether it had an intention to incorporate a "Dislike" button, Facebook officially rolled out "Reactions" to users worldwide on February 24, 2016, letting users long-press on the like button for an option to use one of five pre-defined emotions, including "Love", "Haha", "Wow", "Sad", or "Angry". Reactions were also extended to comments in May 2017, and had a major graphical overhaul in April 2019.
The like button is one of Facebook's social plug-ins, in which the button can be placed on third-party websites. Its use centers around a form of an advertising network, in which it gathers information about which users visit what websites. This form of functionality, a sort of web beacon, has been significantly criticized for privacy. Privacy activist organizations have urged Facebook to stop its data collection through the plug-in, and governments have launched investigations into the activity for possible privacy law violations. Facebook has stated that it anonymizes the information after three months, and that the data collected is not shared or sold to third parties. Additionally, the like button's potential use as a measurement of popularity has caused some companies to sell likes through fake Facebook accounts, which in turn have sparked complaints from some companies advertising on Facebook that have received an abundance of fake likes that have distorted proper user metrics. Facebook states in its Terms of Service agreement that users may only create one personal page, and it has ongoing efforts against the spread of fake accounts.