Knowledgebase

Disallowed Filename Attachments

The following is a list of file attachments that may be blocked by the service (the attachments are removed from emails before delivery to you and placed in a quarantine area for 30 days should you wish to receive them):

# These are known to be dangerous in almost all cases.
.reg Possible Windows registry attack
.chm Possible compiled Help file-based virus
.cnf Possible SpeedDial attack
.hta Possible Microsoft HTML archive attack
.ins Possible Microsoft Internet Comm. Settings attack
.jse_ Possible Microsoft JScript attack
.lnk Possible Eudora *.lnk security hole attack
.ma_ Possible Microsoft Access Shortcut attack
.pif Possible MS-Dos program shortcut attack
.scf Possible Windows Explorer Command attack
.sct Possible Microsoft Windows Script Component attack
.shb Possible document shortcut attack
.shs Possible Shell Scrap Object attack
.vbe or .vbs Possible Microsoft Visual Basic script attack
.wsc .wsf .wsh Possible Microsoft Windows Script Host attack
.xnk Possible Microsoft Exchange Shortcut attack

# These 2 added by popular demand - Very often used by viruses
.com Windows/DOS Executable
.exe Windows/DOS Executable

# These are very dangerous and have been used to hide viruses
.scr Possible virus hidden in a screensaver
.bat Possible malicious batch file script
.cmd Possible malicious batch file script
.cpl Possible malicious control panel item
.mhtml Possible Eudora meta-refresh attack

# Deny filenames ending with CLSID's
{[a-hA-H0-9-]{25,}\} Filename trying to hide its real extension
Examples:
A977FF0C-8757-4E76-8533-482F91946233
000209FF-0000-0000-C000-000000000046

# Deny filenames with lots of contiguous white space in them.
Filename contains lots of white space

# Deny all other double file extensions. This catches any hidden filenames.
Found possible filename hiding
Examples:
.txt.pif
.doc.pif
.doc.com
.txt.exe

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