content: It's a "do not track flag" which gets sent to the server, which requests they not track you, but can't actually prevent this tracking one way or another. As you suggest, Microsoft could use this matter to attack their more ad-driven competitors and I think they did do so in this with one of IE10's selling points being "hey look - our browser has do-not-track enabled by default!" However, as was said at the time, and as they seem to have now accepted, having it enabled by default means that it wasn't actually an explicit choice of the user, and so advertisers could've argued that they should just ignore the do-not-track flag being sent by IE (because they had no way of telling whether the user had made that choice or not). Anyway - it's all moot in any case; I very much doubt anyone will respect the do-not-track flag.