Greeneville City Schools

Instructional Technology Team
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PostPosted: Mon Aug 28, 2006 8:18 pm 
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Joined: Mon May 16, 2005 10:13 am
Posts: 103
Location: Central Office
Inbound attachments are deleted if they contain specified extensions, such as executables. Certain types of attachments pose a security threat for they may easily contain viruses and malicious code. Many of the standard file types are executable files, meaning that Windows will automatically start running them as a program as soon as they are ‘clicked’ on. These extensions were chosen because it is almost impossible to prevent the execution of malicious programs sent to you through our email system if they are of these file types. This has proved to very successful in preventing widespread outbreaks of e-mail viruses. The attachment filter might occasionally change in response to the latest viruses.

Some users have figured out that changing a file extension allows it to sneak past attachment blocking. Our Anti-Spam solution has built in file verification abilities, where the contents of the file can be verified. Non-allowed extensions that have been renamed will not be allowed to pass through. There are other ways of receiving files by using FTP or downloading through a web site.

The key points of clarification:

• .exe files and other extensions are being prevented from entering our email system.

• outbound attachments are not filtered.

• Although the mail may be approved, that does not guarantee you will be able to open the attachment. If the attachment is certified as being virus free, certain attachments, executables in particular, will not be allowed by our mail client settings.

The Greeneville City Schools has established polices for denying specific type of attachments from Internet Mail. The following attachments are blocked from incoming Internet Email Messages.

ade
adp
asf
bas
bat
chm
cmd
com
cpl
crt
exe
hlp
hta
inf
ins
isp
js
jse
lnk
mdb
mde
msc
msi
msp
mst
pcd
pif
reg
scr
sct
shb
shs
url
vb
vbe
vbs
wmd
wmv
wmz
wsc
wsf
wsh
ade
adp
asf
bas
bat
chm
cmd
com
cpl
crt
exe
hlp
hta
inf
ins
isp
js
jse
lnk
mdb
mde
msc
msi
msp
mst
pcd
pif
reg
scr
sct
shb
shs
url
vb
vbe
vbs
wmd
wmv
wmz
wsc
wsf
wsh

These extensions are used for some of the most lethal forms of Computer Viruses. By blocking these viruses we can help avoid significant loss of information to our information resources due to Email-borne viruses. Blocking extensions provides the following benefits.

• Prevents the most commonly known lethal viruses from being received into our email system.

• Prevents newly created viruses that are not yet detected by the anti-virus gateway from being introduced into our email system. While the virus definitions are updated automatically on a daily basis, when a new virus is introduced into the Internet, they often spread worldwide in a matter of hours. Some viruses spread themselves automatically by mailing themselves using a person's address list. Often, all users have to do is open a message and click on the attachment and it automatically launches itself and executes.

• Prevents unsuspecting users from executing a virus and damaging their computer, deleting files on our servers and propagating the virus through the mail system. Many of the most lethal viruses will delete files not only from the user's local PCs but all mapped drives to servers to which the user is attached. This can cause the loss of many documents on multiple servers and spread infections across the system, and beyond, rapidly. Even if the damage can be repaired with extensive virus scanning and restoring lost data from tape backup, hundreds of hours of productivity can be lost from a single viral infection.

_________________
Larry Jones
Central Office


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