Opera has added support for do-not-track in the latest release of its browser, version 12, which became available late last week. The privacy functionality, now supported by all major web browsers, allows users to opt out of online tracking. It's currently up to the individual site whether to honor the user's request, but major web companies have agreed to support the system. Internet Explorer 10 will include do-not-track turned on by default. With the release, Opera also closed six security vulnerabilities, ranging from cross-site scripting to remote code execution bugs.