Recently, antivirus company avast!'s forum was recently compromised by hacker who apparently used a "hole" the SMF software.
More information can be found on the avast! forum: http://forum.avast.com/index.php?topic=34039.0
If legitimate, other SMF forums may be in danger.
There are no known holes in SMF at the moment, although I cannot speak for third party modifications.
My suggestion is to file a security report.
http://www.simplemachines.org/about/security.php