VirusScan Enterprise 8.7.0 > Access Protection Policies > User-Defined Rules
Click New and choose File/Folder Blocking Rule
You can use wildcards in the File/Folder Name to Block
Do some more research on .kht just in case there are some legit uses, also make sure you do the settings for both Workstation and Server at the top of the policy.
There is also Anti-Virus Outbreak Control option where you can make shares read-only or block access all togehter.
Submit a copy of this on up to McAfee so they can make a signature for the file.
Thanks for your helpful information