I have started to notice that when malware infects the Google Chrome web browser it frequently inserts a registry setting to block further updates to the browser. If you go to 'Customise and Control' then 'About Google Chrome' you should see the version number and this will prompt a check for updates. If you see a 'policy has prevented updates' message (I forget the exact wording) and you are using a home machine then you have been infected. Edit the registry and go to HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google . There are no default policies so I have always deleted that entire section to get rid of the problem.
