It is impossible to tell exactly what happened from your description. There are a couple million identified pieces of malware. You probably opened your firewall up to allow outside access to your computer and probably did not keep Windows and all of your applications patched. Cleaning up an infected computer can sometimes be a real daunting task giving professionals a difficult time. Once you get a clean computer, the trick is to keep malware from getting in, not trying to find them several times a day after they are already in. Nothing is perfect, but if you:
1. Keep all of your software patched as soon as the patches are available. Wherever you can, set up the software to automatically update from the vendor. Secunia Personal Software Inspector will help you identify software that is vulnerable.
2. Install a good anti-virus product. Microsoft's Security Essentials is pretty good and is free (not all free anti-viirus software are acceptable). I use that on some computers and my favorite is Eset's Nod32, but it is fairly expensive and only slightly better. Set it to update automatically a few times a day.
3. If you are surfing and see a pop-up indicating you are infected with a whole bunch of bad stuff and are prompted to "Click here" to be disinfected stop immediately. Do not click...and if you happen to do it before thinking, do NOT enter a credit card number. Just close the browser and move on. It is a popular ruse called rogue AV. It will infect your computer (and people pay for the privilege).
4. Be very careful where you surf, there are hundreds of thousands of infected web sites waiting for you to visit. If you've done all the above, you are fairly safe, but nothing is 100%.
5. Don't open e-mails, particularly ones with attachments, that you aren't positive of the source and know that the source wasn't faked (a little hard to determine sometimes).
Oh, and I take it so much for granted, I forgot:
6. If you have a hardware firewall, set it to do Network Address Translation (NAT). This will keep most drive-by hackers out. And, use a software firewall, as well. Microsoft's built-in firewall is adequate and stays out of sight in the background. So many of the others continually ask you whether you want some obscure module to access the internet, or not. Only really good software professionals have any idea, so people get in the habit of always responding OK, which makes those types of firewalls useless and a pain.
Last edited by BWR; 07-15-2011 at 12:53 PM.