Virus that poses as anti-virus help?

Okay so I was googling away when out of no where one of those things where it's pretends to be an anti-virus pops up suddenly so I clicked the "x" in the top right hand corner thinking if it'd just go away no biggie, but nope the little bugger installed something on my computer. It appears to be some sort of anti-virus thing at a passing glance. It's not really of course, just a pain in the ***. It goes by the name "Defender" or something like that. Anyway, this wouldn't be that big of a problem except it won't let me run any programs! I can't use any web browsers, anti-virus protection- anything. I tried running malwarebytes and the things doesn't allow it! Any advice would be greatly appreciated.