Google has decided to change its position on silently installing extensions on Chrome browser. From Chrome 25, external extension installation option in Windows will be disabled by default. Extensions that were installed using this option will also be disabled automatically.
Upon launching Chrome 25 for the first time, it will show a notification explaining the change. Users will also be able to access the list of extensions that were disabled from the notification window.
If a program try to install an extension in Chrome 25 automatically, a notification will pop up asking users for decision. Users can choose to “Enable Extension” or “Remove from Chrome”.
Source: The Chromium Blog