A like button, like option or recommend button is a feature in communication software such as social networking services, Internet forums, news websites and blogs where the user can express that he/she likes, enjoys or supports certain content. Internet services that feature like buttons usually display the quantity of users who liked each content, and may show a full or partial list of them. This is a quantitative alternative to other methods of expressing reaction to content, like writing a reply text.
Like buttons as used by social networks on websites other than their own are often used as web bugs to track user activities for targeted advertising such as behavioral targeting combined with personally identifiable information (PII) and may be considered a breach of browser security and internet safety privacy concerns.
Use on Facebook 
The like button is a feature of social networking service Facebook, where users can like content such as status updates, comments, photos, links shared by friends, and advertisements. The feature was activated February 9, 2009. It is also a feature of the Facebook Platform that enables participating websites to display a button which enable sharing the site's content with friends. When a user clicks the Like button, the content appears in the News Feeds of that user's friends. The button also displays the number of users that liked each piece of content, and may show a full or partial list of those users. This feature may appear differently on mobile web applications. A "Like Box" also allows Facebook page owners to see how many users and which of their friends like the page.
In an average day, there are approximately 2.7 billion unique Likes on Facebook, meaning over 955 billion in an average year.
A lawsuit was filed in Los Angeles in 2010 claiming the Facebook should not allow minors to "like" advertising. Facebook said the suit was "completely without merit."
Rembrandt Social Media has sued Facebook, claiming that the like button violates two patents granted to Joannes Jozef Everardus van Der Meer in 1998.
The Like button is one of Facebook's social plug-ins, which are for use on websites outside Facebook, a feature which launched April 21, 2010, as part of Facebook's Open Graph, an interface for integrating websites with Facebook's social graph. Speaking at Facebook's F8 developer conference on the day of the launch CEO Mark Zuckerberg said, "we are building a Web where the default is social."
Since then the feature has aroused scrutiny over privacy concerns because the social plug-ins allow Facebook to track visitors to participating sites across the web, even if those visitors do not click the Like button, are logged out of Facebook, or are not Facebook users at all. The Like button is implemented similarly to an advertising network, and as more sites participate, gives Facebook a vast amount of information about who visits which sites, and when. When loading a web page which has the Like button enabled, the user's browser connects to Facebook's servers, which record the URL being visited, and the visitor's IP address and Facebook ID (if logged in). In June 2010 Facebook said it anonymizes this information after three months, and does not sell or otherwise share that information. The ACLU of Northern California cautioned website operators to be careful about installing Like buttons because "they're potentially telling Facebook about everyone who visits their web site, every time that person visits their web site."
By September of that year over 350,000 sites were using the Like button.
In August 2011 the German state of Schleswig-Holstein said the button breached German data protection laws and that federal agencies must remove the buttons and similar social plug-ins from their websites. Canada's Privacy Commissioner had raised similar concerns in 2010.
Vulnerability to attacks 
In February 2013, legal action was brought against Facebook by patent-holding company Rembrandt Social Media. Rembrandt owns several patents taken out by Dutch programmer Joannes Jozef Everardus van Der Meer, who died in 2004. These include patents filed in 1998 relating to van Der Meer's fledgling social network Surfbook, including, according to legal papers filed by the patent holder, the ability for users to approve data using a "like" button.  
Google Search has a +1 button for endorsing web pages in search results. (The name "+1" is Internet slang for "I like that" or "I agree".) In August 2011, Google integrated its +1 button to its competing social networking site Google+. The social microblogging site Twitter also launched a "Follow" button around the same time.
In culture 
- "Facebook privacy probed over 'like,' invitations". CBC News. September 23, 2010. Retrieved August 24, 2011.
- Albanesius, Chloe (August 19, 2011). "German Agencies Banned From Using Facebook, 'Like' Button". PC Magazine. Retrieved August 24, 2011.
- Zawinski, Jamie (founder of the Mozilla Foundation) (02011-09-02). "Surprise! Facebook doesn't like privacy countermeasures". JWZ.org. appliedops.net.
- McCullagh, Declan (June 2, 2010). "Facebook 'Like' button draws privacy scrutiny". CNET News. Retrieved December 19, 2011.
- Arrington, Michael (March 25, 2010). "Facebook To Release a "Like" Button For the Whole Darn Internet". TechCrunch. Retrieved December 29, 2011.
- Porterfield, Amy; Khare, Phyllis; Vahl, Andrea (2011). "Chapter 3: Better Engagement with the Help of Facebook Like Links and Buttons". Facebook Marketing All-in-One for Dummies. John Wiley and Sons. ISBN 0-470-94230-4.
- "Like Box". Facebook Developers. Retrieved 24 August 2011.
- "Like". Facebook Help Centre. Retrieved 24 August 2011.
- "There were over 955 billion Facebook Likes this year". Facebook Marketing Blog. 7 February 2013. Retrieved 3 March 2013.
- "Lawsuit says teens too young to "Like" Facebook ads". France24/AFP. 27 August 2010. Retrieved 24 August 2011.
- Facebook sued over 'like' button - BBC, 11 February 2013
- "Social Plugins". Facebook Developers. Facebook. 19 December 2011. Retrieved 19 December 2011.
- Siegler, MG (April 21, 2010). "Facebook: We'll Serve 1 Billion Likes on the Web in Just 24 Hours". TechCrunch. Retrieved December 19, 2011.
- Fletcher, Dan (April 22, 2010). "Facebook Looks to Get Personal". Time. Retrieved December 19, 2011.
- Gelles, David (21 September 2010). "E-commerce takes instant liking to Facebook button". Financial Times. Retrieved 24 August 2011.
- Yin, Sara (15 December 2010). "Microsoft Adds Facebook 'Likes' to Bing Search Results". PC Mag. Retrieved 25 August 2011.
- Yiu, Paul; The Bing Team (15 December 2010). "Bing Feature Update: Discover more things your Facebook friends like". Bing Search blog. Microsoft. Retrieved 25 August 2011.
- Perez, Sarah (1 June 2010). ""Likejacking" Takes Off on Facebook". ReadWriteWeb. Retrieved 24 August 2011.
- BBC News - Facebook sued over 'like' button
- United States Patent: 6,415,316 - Method and apparatus for implementing a web page diary
- United States Patent: 6,289,362 - System and method for generating, transferring and using an annotated universal address
- Newman, Jared (24 August 2011). "Google +1 Now Links to Google+ Profiles: Let the War on Facebook's 'Like' Button Begin". PC World. Retrieved 24 August 2011.
- Bazilian, Emma (June 1, 2011). "Twitter and Google Launch Their Own 'Like' Buttons". Adweek. Retrieved December 19, 2011.
- No me gusta - Un Techo para mi País, Campaña 2010