Absolutely a troyan, someone is controlling you computer, I suggest you to do this:
- Change all your passwords: Runescape, MSN, facebook, myspace, whatever... IN OTHER COMPUTER (Because he/she will still get your password even if you change it, in that PC).
* Do not type any password on your PC after changing them.
- Scan your computer with Kaspersky (Online) and your actual antivirus.
- If you find a/some virus/viruses, then PROBABLY you got rid of the virus. Otherwise, I suggest you to format your PC.
- After this, install a good antivirus: Nod32, Kaspersky, BitDefender, Avast or AVG. No McAfee, Panda or Norton shit.
- Optional: You could read about viruses and troyans, so you could PREVENT this type of inconvenients.
I hope I have helped you.