We reported today that Twitter has begun implementing the "Do Not Track" privacy option for its users, and we're now getting a better idea of why the company may have rolled it out: it's testing "who to follow" lists custom-tailored for users based upon their browsing behavior. As the company details in a blog post, Twitter currently offers up the same user suggestions to all new users. The revised system, however, utilizes the entire "Twitter ecosystem" — namely, actions within Twitter as well as any website that has integrated Twitter buttons or widgets. It looks at which Twitter users follow other users, and then combines the information with both your and other users' browsing information. "By recognizing which accounts are frequently followed by people who visit popular sites," Twitter writes, the new system can suggest users with similar interests.

Twitter is quick to note that it is easy to opt out of the new system — hence the Do Not Track functionality — and that new users will have to intentionally turn the service on. Additionally, the customized suggestions only utilize the last 10 days of "Twitter ecosystem" behavior. Of course, with any feature like this, it becomes a balance of perceived loss of privacy versus increased utility. That verdict won't be clear until people actually begin using the new lists. If you'd like to try them out for yourself, you can activate the service on Twitter's preview page.