Twitter tracks its users' browsing habits.

Twitter announced Thursday that it will use information it collects about users' browsing habits across all sites with Twitter "share" buttons to recommend accounts to follow.

By tracking individuals during their visits to websites in what the social media site calls the "Twitter ecosystem" (which includes any page with an embedded Twitter widget), Twitter can monitor what stories or topics each user visits most, and use that data to suggest accounts that match their interests.

"We receive visit information when sites have integrated Twitter buttons or widgets, similar to what many other web companies -- including LinkedIn, Facebook and YouTube -- do when they’re integrated into websites," Twitter wrote in a blog post. "By recognizing which accounts are frequently followed by people who visit popular sites, we can recommend those accounts to others who have visited those sites within the last 10 days."

Twitter deletes or aggregates the data it collects after 10 days, and users have the option to opt out of having the their browsing tracked (for more on how to do that, see here or here). In the same blog post announcing its "experiment" with tailored suggestions, Twitter also declared its support for a Do Not Track option and said it would not collect data on users who had enabled the setting on their browsers.
Though other web giants, such as Facebook, also track individuals as they peruse the web, Twitter's disclosure was seen as a surprising -- and unwelcome -- admission by some.
http://www.huffingtonpost.com/2012/05/18/twitter-tracking_n_1526244.html

Irony: Twitter is the latest web giant to support Do Not Track.

Ed Felten, chief technology officer at the Federal Trade Commission, announced today at an Internet Week privacy panel that Twitter will now stop tracking user data from those who opt-out. According to The New York Times, which was first to report on the news, Twitter's tracking will be nixed with help from Firefox's Do Not Track feature.

Twitter confirmed Felten's statement in a tweet today, saying that the company "now supports Do Not Track." Twitter also commended the FTC for its "leadership on Do Not Track."
Do Not Track has been met with both criticism and appreciation. The issue, critics say, is that even if a user has the Do Not Track feature turned on in their favorite browser, the only way it'll work is if a Web site also supports the technology. Privacy advocates, including the FTC, say that Do Not Track could be a fine way for Web users to control how their surfing behaviors are tracked. They also point to an increasing number of Web sites supporting the privacy measure.
http://news.cnet.com/8301-1009_3-57436330-83/twitter-announces-support-for-do-not-track/