In addition to the above there are a couple of online virus checkers you can run to see if you are still infected, because if it is a trojan (or worse a rootkit) it may still be hiding. So this is what you should do.
Make sure your AV is updated to the latest definitions and run it. If that gives you a name for the virus then you have something to target.
Run an online virus scan, quite a few virus/malware/spyware etc can 'hide' from a 3rd party AV but seem to have more problems with one run offsite from the actual computer, they can't latch on to the executing files you see. I'd suggest Panda or Trend Micro, they are both pretty good.
If both of those show clean you're probably doing ok. However I would also get a copy of Malwarebytes, it's free to use, if you want the resident protection and automatic updates you have to buy a licence, but you don't need that to run it and you can update it yourself weekly.
Once you have installed that run it. Full scan, it's designed to specifically target malware and it does it very well. If that comes up clean you are 90% there.
I don't know what resident protection you have on your system but I would also suggest spybot s&d, that is also free (once again you need to do manual updates) and targets spyware primarily and pretty much everything else on a secondary level and it does have an active resident programme that will monitor your browers use full time. I would not suggest installing the TeaTime add on that monitors everything and can sometime slow down a system simply because of the amount of work it is doing.
With those above you'll be pretty covered, just make sure you keep them up to date.
Oh and get a good pop-up blocker, with one of those configured properly this may not have happened. I'm not sure what browser you use but if it is IE change it, some 'ware specifically target that browser. I'd suggest Firefox. If you are already using that then make sure you install the AdBlockPlus add-on. It stops a lot of these problems in their tracks.