You may have contracted a "Worm". Do you know what File you downloaded right before this happened. If so PM me. See the Links below.
Try this 1st.
Limewire Acting Wierd (PLEASE HELP!!!)
If no help then try here.
This is probably one of the best help Forums for Malware I've found. Just another suggestion.
Malware Removal - MajorGeeks Support Forums