Thanks very much for your reply. I've been trying to enable the preference in Google Chrome Canary on Mac OSX. However, I haven't been able to successfully block the IP leak - I suspect because I haven't configured it correctly. I had to manually create the file "/Library/Google/Google Chrome Master Preferences" and add the setting you suggested. I then reinstalled Chrome Canary and tested but no effect. I also tried editing the user preferences file in ~/Library/Application\ Support/Google/Chrome\ Canary/Default/Preference but that seems to be overwritten by the browser. How should I be configuring this preference? Thanks again.