Malwarebytes is a good program, I can recommend it, grab it and let it give your system a scan, it's pretty good at finding nasty stuff. The problem with viruses like the one described in the OP is, like Skybird has said, they can be very hard to fully get rid of, especially rootkits and the like, it's like a weed, you can cut the stuff above ground, but unless you pull it up by the roots, it's not going away.
Another good bit of kit is Firefox with the noscript addon installed, gives you a lot more control over what scripts run on your page, because even internet adverts can carry viruses in them now, I've been got that way a couple of times before I got noscript and Malwarebytes.
Obviously precaution is also a potent weapon, I've had a few of those Costco emails recently, but they've all fallen into my junk folder, I'll say this for Hotmail, it's got a pretty smart filter.
