Future versions of Apple's Safari browser may contain a 'Do Not Track' feature that stops advertisers from following users around the web.
Safari's Do Not Track feature has already appeared in the test release of Mac OS X Lion, the Wall Street Journal reports. Lion launches this summer, but it's not clear whether Safari will get the feature sooner, or whether it'll be available to Windows users.
The tracking of behaviour on the web has become a heated topic. After a series of Wall Street Journal articles described how advertisers follow users across the Web and build targeted ad profiles, Mozilla added a Do Not Track feature to Firefox 4, and Microsoft added Tracking Protection to Internet Explorer 9.
But the notion of Do Not Track is interpreted differently by the browsers that currently use it, and the Journal doesn't say whether Safari's version uses the Do Not Track standard from Stanford University, or some other implementation. Here's a rundown of how other browsers work:
Firefox's Do Not Track feature, found in the browser's preferences menu, uses an http header to tell websites that the user doesn't want to be tracked. The idea is for Web developers to build the appropriate response into their sites, something that's not going to happen overnight but could be useful in the long run. This is an implementation of Stanford University's Do Not Track standard.
Internet Explorer 9's Tracking Protection requires the user to add lists of trackers to block, provided by third parties. Like Do Not Track in Firefox, this feature relies on the good faith of advertisers to honor the user's request, but it's more effective in the short term because tracking protection lists don't require any new code from websites. Microsoft has said that IE9 will offer Do Not Track as a secondary method. It's automatically enabled when you turn on the Tracking Protection feature.
Finally, there's Google Chrome, which doesn't have a Do Not Track feature built into the browser. Users can, however, install the 'Keep My Opt Outs' extension, which remembers privacy preferences even after clearing the browser's cookies. Users will still have to use third-party services, such as AboutAds.info, to opt out of ad personalisation and related tracking.