Overall common sense is the best tool you can use. If it's a family computer then common sense is probably a lost cause, so set up separate users to protect your own data at least.
Oh, wow, I'm necroposting in such an old thread of mine . . . but it is relevant I promise. My sister caught a nasty virus. Thankfully, it seems to only be affecting her account (as in, thankful I can still access the internet). I had hoped that she would be more tech-savvy . . . but then again, Internet Explorer 6 is my father's browser of choice so . . . Suffice to say, I ran SuperAntispyware and removed a number of nasties, and ran a full scan on malware bytes (which didn't find anything) but things have only slightly improved. I also ran avast and it detected a few more but wasn't able to get rid of them.
The virus in question is 'xp defender', which I'd recognized upon seeing the pop-ups; our Aunt and cousins had had a similar problem on their home pc once. They never fixed it because they were getting a new laptops for each other anyway so I can't call them up because they wouldn't know.
Yes, what now? Your help is welcome and appreciated.