Another member was asking some very similar questions a couple of months ago,
here's the thread. I'd suggest taking a quick (yes, relative term

) look at it, particularly my suggestion
here.
One easy way to make sure its not the 'Conficker' virus is to take a look at
this page. This conficker infection test will show if security or anti-virus related sites are blocked from your browser, indicating there is a decent chance you're infected if they are. It's not fool-proof, but it's a start.
Lastly, I'd suggest another A/V tool than MacAfee, even ClamAV and AVG work much more efficiently in my experience.
Good luck, let us know how you make out... -TD