Google images virus?

Three time in the past month or so, we've run across a bad image link in google images.

What happens is you do a search for pictures in google images....and mind you, these are "innocent" searches. (1st was a pic of a toy, 2nd was a pic of a dog, 3rd was a pic of John Lennon). Then, when you click on the image thumbnail, instead of it taking you to the site where the image is located, it takes you to a site that looks like a Windows security page, and it calls itself something to the effect of "windows security software", it looks like it's doing a scan, and it says it found 4 virus infections.

It's scary to encounter this....I quickly close out firefox (oh, by the way, we have up to date security software & firewall, and one computer has a windows 7, the other has windows xp) and clean out browser history, and run scans...and scans show up clean.

My question is - am I really clean? The computer seems to be functioning ok. Hopefully this fake security site really didn't download anything? Anything else I can/should do to really ensure that computer really is clean?

Also, anything we can do to prevent from accidentally clicking on infected image links? Anything we can do to block them? Why doesn't my firewall & AV & spywareblaster software block it? (on this windows 7 computer, Microsoft Security Essentials is installed....should I switch to something else?)

Also, I searched the internet to see if others were encountering the same issue, and apparently this google image fake virus scan problem is rampant. Anything we can do to stop/block/prevent it?