OK Guyz

OS will not change a file XXX to YYY just 'cause its MP3 or JPG. You sure
are infected with a worm/virus. No there are so many variant around so it's
difficult to tell which work of script kiddie is eating your patience. My
suggestion is install good anti-virus on your system like McAfee or Norton;
Make sure you let Memory resident (Service) virus montior ON. And ofcourse
keep Virus Definitions uptoDate.

This should solve current problem and future ones too

Regards,
Sanjeev