We have been getting hits by spammers using personal messages for about a week. Unless you report them we Admins don't know about them so can't do anything.
Please read post #2 on this thread from a few days ago on how to report them so we can ban them. We have also taken a few other step to help curb them, but it is difficult to do while preserving privacy on Personal Messages. http://www.homemodelenginemachinist.com/showthread.php?t=26501