hi all. a friend has been stuggling with a virus for a while, and it seems to have found it's way into my machine too, most likely when he connected to my wifi or perhaps we just downloaded the same thing
using windows 7 ultimate 64 bit, and firefox, in both cases
The virus manifests itself, seeminly with some randomised chance to trigger (feels like about 25% of the time), when i attempt to load any page on certain popular sites. most notably i'm seeing it on google, youtube, and gmail, (and pages on those sites are taking abnormally long to load, maybe related)
the main symptom is a little popup dialo which steals focus and says something along the lines of "Your flash player may be out of date, please update!" Then it displays a spoof of the adobe flash download page, replacing the content (but not the url) of the page,.
in some cases, particularly with videos, it will replace only a part of the content (the video itself) which looks silly.
i've tried avast antivirus so far, with a full clean report. please advise other basic tools and diagnostic steps to try