Abstract: Security fixes and feature improvements don't benefit the end user of software if the update mechanism and strategy is not effective. In this paper we analyze the effectiveness of different Web browsers update mechanisms; from Chrome's silent update mechanism to Opera's update requiring a full re-installation. We use anonymized logs from Google's world wide distributed Web servers. An analysis of the logged HTTP user-agent string that Web browsers report when requesting any Web page is used to measure the daily browser version shares in active use. To the best of our knowledge, this is the first global scale measurement of Web browser update effectiveness comparing four different Web browser update strategies. Our measurements prove that silent updates and little dependency on the underlying operating system are most effective to get users of Web browsers to surf the Web with the latest browser version. However, there is still room for improvement as we found. Chrome's advantageous silent update mechanism has been open sourced in April 2009. We recommend any software vendor to seriously consider deploying silent updates as this benefits both the vendor and the user, especially for widely used attack-exposed applications like Web browsers and browser plug-ins.