As others have said:
What Viri/malaware scanner were/are you using?
Are you logged in as admin or a reg user? Did you nerf the UAC?
What software was installed recently, was it ad supported, was it browser bar supported? was it licensed legally(no key gens/no full version download here)?
What online games did play, what FB game did you play?
How many YouTube videos did you watch, did you click on any links to make a banner or other screen clutter go away on those ads/games?

You could easily title the thread as Windows + Safari/IE/Opera/Chrome/FF = Virus
When it actually should be Windows + AVG(or what ever Viri/malware scanner you are using) = Virus