Tech Tips - Why do some of the email messages I send or receive show that a virus was blocked?

If you are using the district email system (using Outlook or Outlook Express to receive your shelbycs.k12.in.us email), all the email is scanned by one of our servers for computer viruses or worms.  This scanner has two levels of security:  

Known Viruses: It will scan based on the set of known viruses.  The server will scan all email attachments to see if it matches any of the known viruses that have already been identified.

Preventive Blocking: The server will also block attachments based on what type of file extension the attachment contains. A file extension is part of the file's name and is the section that usually follows a period or dot and indicates the type of information stored in the file. For example, in the filename EDIT.DOC, the extension is DOC. The DOC indicates that the file is a Word file or document.  If the file name is Investor.PDF, the file name is Investor and the extension is PDF, which stands for Portable Document Format which is used by Acrobat Reader.

While .DOC and .PDF files are common and rarely a real risk (although there are Word macro viruses that can attach themselves to DOC files), there are other less commonly used file extensions that are notorious for being associated with computers worms and viruses.  Our server will automatically block attachments that have these less commonly used file extensions, since there is a greater risk that a new or undiscovered virus or computer worm could be hidden in the file.

Considering the fact that a new virus could spread undetected for a week or more and even after the virus is discovered, another week could pass before a virus definition could be created to store on our server that scans for known viruses, there is the real threat that a new virus or computer worm could be sent to our district's email server before a virus definition is ready for use.  This happened twice between November 2001 and March 2002, when very new viruses were sent to people in our district and the only reason we prevented an infection in the district was due to the fact we blocked the right file extension.

Security Setting in Outlook Express 6.0 - There is also a security setting in Outlook Express that also blocks far too many attachments.  To see how to change that Security setting, go to Tech Tips - Outlook Express blocking too many attachments.

Below is a list of file extensions we block.  If you are trying to receive a legitimate file that happens to have one of the blocked extensions, please feel free to contact the Technology Department and we will be glad to try and assist you.

File Extensions We Block as of May 1st, 2002

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