The good news is that you don't have a virus. You have adware, which is intended to scared you into thinking you have a virus. Virus software won't typically find adware.
Also, you should note that some very popular anti-adware software will not find it either, because the adware is programmed to hide itself by using file names of those popular software programs. Tricky, tricky, tricky.
Solution is to download free version of Malwarebytes Anti-Malware from Cnet.com, as stated by castlesofsand. Run that and it should clear it. You would also do well to run it once a week or so.
Are you still using Internet Explorer? Ditch that crap and download Mozilla Firefox to use as your browser. This, too, will help fight against the pop-ups.
Unless your computer goes to blue screen with a bunch of coded text when you turn it on, the above should work. If the puter gets locked down, it takes a bit more trickery to get rid of it, but it is also very doable.
