As a small business owner who deals with this for a living, I’d say: do a reload. Save all your data on an external drive, then reload all your operating systems and programs. Then update them all.
You may never be able to find out where you got it, but be sure to have antivirus, spyware, and malware detector programs on your system and keep them up to date. If you don’t have all of them, get them.
Of course, you could always call a pro if you don’t have a spare 6 to 8 hours ;)
I do have all of my data on a separate drive from the OS, it’s more the pain of reloading all of the programs. I use 3 different scanners and it beat all of them. Even the remote scanner on Trend Micro doesn’t get rid of it.