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Originally Posted by squeeeb
one fear i have is the virus (if there is one) will tell the anti-virus it's an ok program, and the anti-virus won't detect it. is that even possible?
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Yes and no. I'm going to try to answer this without getting overly technical, but I'm not sure I can.
Modern anti-virus programs generally use several methods to protect your computer. One common method is to use definitions; basically, the company producing the AV program maintains a list of virii. The company will periodically publish updates to the list and the program on the user's computer will connect to the server and download the updates; this typically happens once every 24 hours, although that's by no means set in stone. In fact, Kaspersky is known for it's particularly fast response time, with updates for an infection usually coming within hours of the new threat being spotted in the wild. This is what I was alluding to above; if you've managed to catch a brand new virus that hasn't been included in the definitions yet, all you really have to do is wait; when the definitions are updated to include your little friend Avast! (or Kaspersky, or whatever you're running) will be able to pick it up and deal with it.
Virus coders, though, they're crafty. They sometimes employ techniques to try to fool the anti-virus programs; this can include things like encrypting part of the program or writing adaptive or self-modifying code. This can make pinning the virus in the definitions a bit tricky. As well, the clear downside to the dictionary approach of keeping a list of known virii is that there's a lag between a new virus being released and the definitions being updated to catch it. For this reason, your typical AV software will use what's referred to as a heuristic approach as well. The specifics of this are a bit more in-depth than I'm really willing to talk about just now, but the broad overview is that the program monitors processes for suspicious activity and flags them if they 'act like a virus.'
Early anti-virus software was also periodically subject to direct attacks; the virus would actually modify and/or disable part of the program in order to be able to run unimpeded. Again, technology has adapted and modern software contains self-integrity checks to prevent this from happening.
So in other words, yes what you said is possible. Sort of. But it's not terribly likely.
Also, what I meant when I said don't blame the porn was precisely that. Porn is generally either pictures in the form of jpegs or video in the form of mpegs or avi files. All of these are simply container files and cannot carry malicious code any more than a book can carry your groceries. If you have caught a virus, it'll be from a seperate source.
And finally, I neglected to ask first but will correct this oversight now; have you run checks for adware or other forms of malware? Sometimes virus-like symptoms can come from malware that isn't actually a virus. Kaspersky has a full protection suite that catches spyware and adware, but Avast! doesn't. So if you haven't actually installed and run Kaspersky yet, there's a possibility you've got something else on there.
EDIT - What the hell. I've already typed all this crap out, I'll do the whole nine for ya. If you're still convinced you may have a virus, go run
HijackThis! and post the log here. I'm not a big fan of poring through logfiles when I'm not getting paid to do it, but there's no sense in going this far and then stopping.