Recent advance in web tracking technologies has raised many privacy concerns. To combat users' fear of privacy invasion, online vendors have taken measures such as being more transparent with users about their data use and providing options for users to manage their online activities. Such efforts gain users' trust in online vendors and improve their willingness to share their digital footprints. However, there are still a significant amount of users who actively limit involuntarily sharing of data because vendor provided management tools only restrict the use of collected data and users worry vendors do not have enough measures in place to protect their privacy sensitive information. In this paper, we propose TrackMeOrNot, a new anti-Tracking mechanism. It allows users to selectively share their online footprints with vendors. With TrackMeOrNot, users are no longer concerned with privacy. Using it, users can specify their privacy sensitive activities and selectively disclose their activities to vendors based on their specified privacy demands. We implemented TrackMeOrNot on Chromium browser and systematically evaluated its performance using a large set of test cases. We show that TrackMeOrNot can efficiently and effectively shield privacy sensitive browsing activities.