The third-party cookies used by advertisers and their agencies to track web browsing activity are under attack. Browsers like Firefox and Internet Explorer try to block the years-old technology with "Do Not Track," and now internet behemoths are looking to replace cookies with their own tracking technologies. The newest entrant, according to Ad Age, is Microsoft, which sources say is working on a technology that could track users across Windows computers, Bing, Internet Explorer, Windows Phone devices, and Xbox consoles in order to serve highly targeted ads.

Microsoft said in a statement to the website that "We agree that going beyond the cookie is important. Our priority will be to find ways to do this that respect the interests of consumers." However, the primary interest is likely in filling the gaps where cookies fall short, like on mobile, consoles, and streaming video services, where they have limited to no ability to track user activity.

Mobile activity is largely lost by third-party cookies

It's not clear when Microsoft's cookie replacement will be ready, according to Ad Age, though it's said to be in the early stages. There's also little information available about Microsoft's specific plans, but what's understood so far is that it will function as an identifier connected to individual devices. It's unknown if the technology will be limited to the company's services and devices, but it's believed that the tracker could have fewer privacy concerns as Microsoft would be directly responsible for user data, rather than the array of companies involved with the current standard.

Just last month, reports revealed that Google was working on its own cookie replacement, called AdID, which would have more granular privacy controls as well as the ability to more fully track mobile usage. Apple is involved as well: it uses its own tracker, called Identifier for Advertising (IDFA) on iOS devices, and it's long blocked third-party cookies in Safari. Facebook, meanwhile, can track users with its universal login tools across many websites. Both Google's and Microsoft's projects are far from completion, but it's very possible that the future of web tracking may revolve around a handful of proprietary tools from the largest companies that promise increased privacy as well as better tracking for advertisers.