Do you ever receive a strange Messenger message from your friend, but you did not have MSN Messenger open? Chances are, the default Windows Messenger 4.7 is the culprit. No, this is NOT MSN Messenger, which is at version 7.5 as of this writing. You can’t get rid of this via the Control Panel and must resort to a special command.
Remove that pesky Windows Messenger!
From your Start Menu, select Run, then copy and paste the entire following line into the box:
Press Enter – you will see flashes of the progress bar moving.
This will remove Messenger for good. After your next reboot, you won’t have to deal with these "mysterious" Messenger windows anymore.