I recall that the problem started when I allowed FireFox to do an automatic update. The update included an new version of FlashGot (which I never use, but hey) and a prompt to download the latest Adobe Reader, which I did. Firstly, FireFox started behaving strangely, freezing or closing at random, forgetting passwords and so on. I even deleted the program and installed a fresh download, but with no success. A week or two later, it started really buggering me about. Google searches were redirected to sites I didn't want, and after closing the Google page (the only way out of the problem) and retrying the search, I got a blank screen with the message from Google that my machine was sending out automated requests and that no further searches were possible. A full restart was the only way round it - until the next time.
I identified this as a browser hijack, although I wasn't able to find the name of the virus. It must have been one doozy of a program, as it was impervious to all attempts to remove it. I spent a day doing this sequence:
- Update all AV and similar programs with latest definitions
- Disconnect network cable
- Run Avast and AVG anti-virus programs
- Run Adaware and Spybot S&D anti-malware programs
- Run Avast boot scan from cold start.
When I read the advice linked above, it all made sense. In my case, it was Adobe Reader rather than Flash that was the bait, but everything else fits. It seems as though I was fooled into downloading and running a virus, when I thought I was updating programs I trusted. I feel pretty foolish, as although I am by no means an expert in these things I am usually quite smart about checking things, not opening unrecognised programs and so on, and my PCs have been free of any serious virus attacks for several years.
So, if you run FireFox and it prompts you to upgrade anything after it has finished updating, pause and follow the advice in the link. It may save you a lot of hassle.