Posting this because I have seen recent reports that some attackers are starting to use "CHM" files to drop malware.
CHM is a very old file type that was used to include compiled help screens in Windows applications.
The file type appears to continue to be supported by Microsoft, hence there is the possibility that such files may be "automatically" opened by some applications if they are attached to an email.
I just want to remind everyone that SMG properly detects CHM files using it's true-type engine, hence provides the capability for you to create fileterning policies that can act on CHM file attachments.
Add Attachment List -> Add Attachment Type -> If the True file type -> Encapsulation Format -> Microsoft Compiled HTML Help (.chm)
Hope you find this useful.