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Internet viruses and worms spread
by e-mail are becoming more and more common these
days. If your school uses email regularly it
is especially vulnerable, since an infection in one
computer can quickly spread throughout the internal
network. In addition to getting a good antivirus
program, following a few simple rules will help to
ensure that you don't become the next victim.
First, understand that just because
an e-mail appears to be from a trusted source,
doesn't mean that it really is. Viruses and
worms spread by automatically sending emails from
the victim's computer to other e-mail addresses that
it finds on that computer. For instance, if
Joe is in Bob's address book and Bob gets a worm,
then Joe may receive a message containing a copy of
the worm from Bob's computer.
To make matters worse, an e-mail
containing a virus or worm may have the sender's
address forged, meaning that you have no idea where
the message really came from.
Beware of any messages that contain
an attachment and use vague language such as "Please
see attached for details" or "Thank you". Some
messages will even go as far as to include a message
saying that the attachment has been scanned and
certified to be virus free. Don't believe it!
When in doubt, try to contact the message sender to
see if they really sent the message.
Another thing to remember is that an
e-mail message itself cannot hurt your computer.
The danger occurs when you try to open the
attachment in the message.
So, how do you know which attachments are safe to open
and which aren't. One way to tell is by the
file extension (the last three letters after the
period in the name). Here's a brief guide to
let you know what's safe, what isn't, and what is
borderline: |
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Executable files and macros
(files ending in .exe, .com, .bat, .vbs, or .cpl):
Never open these unless you are 100% sure
they are from a trusted source, and have been
scanned for viruses. These types of files are
very commonly used to spread viruses and worms.
Zip archives (files ending in
.zip): A zip archive is a file which contains other
files in a compressed format. A zip archive by
itself will not hurt your computer. However,
the files inside the archive could be dangerous.
Zip files are becoming more and more common as a way
to bypass virus scanners, so treat them with
caution. Make sure the zip file is from a
trusted source, and doesn't contain any files within
that could be dangerous.
Word, Excel, and PowerPoint documents
(ending with .doc, .xls, or .ppt): These files may
potentially contain macros which can harm your
computer. Before opening them, make sure your
Microsoft Office
security settings are configured to
either block macros or prompt you before running
macros. Never run a macro from one of these
files unless it is from a trusted source.
Image files (files ending
in .jpg, .jpeg, .gif, or .bmp): These files cannot
harm your computer, and are safe to open.
However, if you have children in your household, be
aware that pictures from an un-trusted source may
contain adult content.
Internet documents and links
(ending with .htm or .html): Before opening these,
make sure your browser's security settings are
adequate. For Internet Explorer, this means
setting the security level to at least "medium"
using the Internet Options control panel. If
you receive a prompt when opening an unfamiliar web
page which asks you if you want to install and run a
particular program, always answer "no" until you
have determined that the site is trustworthy. |
