• by Wendy Davis  @wendyndavis, May 17, 2012

Twitter has joined the growing roster of Web companies that have promised to honor users' browser-based do-not-track requests.

The micro-blogging service said on Thursday that it will refrain from collecting data about users who have activated do-not-track when they visit outside sites with "tweet" buttons.

Twitter informed users about its support for do-not-track in a blog post about a new feature that will recommend followers to users based on people's activity throughout the Web.

"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 Web sites," Twitter says in a post explaining its recommendation engine. "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 says that users can opt out of the new feature by activating a do-not-track header or through their Twitter account settings.

"If you have DNT enabled in your browser settings, we will not collect the information that enables this feature, so you won’t see any tailored suggestions," the company wrote. "We hope that our support of DNT highlights its importance as a privacy tool for consumers and creates even more interest and wider adoption across the Web."

Twitter's decision to honor browser-based do-not-track requests was announced at an Internet Week New York event on Thursday by Ed Felten, the chief technologist at the Federal Trade Commission.

Since December 2010, the FTC has been urging the ad industry to offer users an easy way to opt out of online tracking by third-parties that have presences on sites users visit.

News that Twitter won't collect data from people who have activated do-not-track was generally well-received by privacy advocates, as well as some lawmakers. Sen. John Kerry (D-Mass.) said the announcement "proves that exercising respect for people’s choices on how, when and where to have their information collected is something that responsible, competitive companies can do."

Rep. Ed Markey (D-Mass.) tweeted his support for the company, calling it an "industry leader" and urging other companies to "give consumers right 2 say NO 2 info collection."

For at least 10 years, ad networks have offered opt-out links that users can click on to communicate that they don't want to receive behaviorally targeted ads. But those opt-outs are cookie-based, which means they get deleted when users erase their cookies. By contrast, a browser-based header would remain active until consumers affirmatively turn it off.

The ad industry doesn't require companies to stop collecting data about users who opted out of behavioral advertising, only to cease sending them targeted ads.

The self-regulatory group Digital Advertising Alliance said in February that it will require members to honor the do-not-track headers, but there's not yet a consensus between the FTC, Web companies and privacy advocates about what types of data can be collected from users who don't wish to be tracked.

FTC officials have said that an effective do-not-track system requires companies to cease collecting most -- though not all -- types of data from consumers who don't want to be tracked. FTC Chairman Jon Leibowitz recently told lawmakers that he envisions exceptions for purposes of fraud detection or frequency capping, but is wary that an exception for market research might prove too broad.

Browser manufacturers only recently began offering users do-not-track headers that can be activated. The header communicates users' preferences to Web companies, but it's up to Web companies to decide whether to honor the headers. In March, Yahoo said it intends to follow do-not-track headers.

Currently, around 12% of desktop users of Firefox in the U.S. have activated a do-not-track header on a PC, Mozilla's privacy head Alex Fowler said on Thursday. Mobile adoption is even higher; more than 30% of U.S. Firefox mobile users have activated the setting, Fowler said.