Microsoft Anti-Spyware just found trojan.backdoor.small.fb

[scrub]

This just showed up on a daily scan. I run one every morning, so it shouldn't have been on my computer for more than a day. I had MAS delete it, and running Spy-Bot and Ad-Aware didn't find anything. I'm about to run a full AV scan.

I haven't had a lot of success googling to find out what this thing does. If my AV comes up clean, should I do anything else? Specifically, should I change my passwords and/or reinstall my operating system?

Thanks.

scrub