Sorry, but I have to disagree with 666philb
antivirus program is 100% effective, so assuming that just because yours doesn't find anything, everything is OK, could be a big mistake.
Which is more important to you; loosing a little time to be reasonably sure you're free of infection, or possibly loosing a lot of time reinstalling your OS, and maybe loosing all of your applications, and personal info.
Then again, you may be one of those people that don't mind reinstalling everything, when they develop a problem.
I'm not, one of those people.
If I don't suspect a problem, I run an online scan once a month.
If I do, or one of my security programs detects a problem, I will also run an online scan, just to be sure.
I don't like taking chances with all of the info (approx. 2TB)
I have stored on my system, if I don't have to.
The risk to me, is just not worth it, not to mention the time it would take to replace all of the info from backups.
I use the ESET Online Scanner
, or the Kaspersky Online Scanner
Both links can be found in the Freeware Replacements For Common Commercial Apps
topic, in post #1, under Free Online Virus/Trojan/Spyware Scanners
You'll find a few other scanners there, that you may want to try.