I can't believe it; this has happened to me twice this weekend. Your computer is most likely infected with trojans. Don't worry, I have been able to get rid of them using Malwarebytes' Anti-Malware, which can be download
here (click cancel for Language Pack Installation if that comes up).
Perform a quick scan, remove all items at the end, and then reboot to remove additional trojans if prompted.
If you have any other questions let me know!
-Soccer