A few random remedies are
- Get an Anitvirus program
- Run a full system scan and remove the virus
- Delete the infected file
- Use system restore (Win XP)
- Reinstall the OS (not recommended, only use as a last resort)
You probably should download an antispyware removal program and run it. I recommend MalwareBytes (malwarebytes.org). It's free. Make sure to update the program before running and run a full scan using Windows Safe Mode (Reboot PC and press the F8 key a couple of times before the Windows screen appears. Enter Safe Mode, or Safe Mode with Networking if you need network access).