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July 28, 2006
What’s Attached to That E-mail?
Dear Larry,
I always see a message when I open an attachment to one of
my e-mails asking if I think it is safe. I just started wondering how would I
even know if an attachment were safe or not?
P. P.
Dear P. P.,
Good question...one that I’ve addressed in the past, but it
bears repeating. When I ask my clients if they’re careful about opening e-mail
attachments, they often respond by saying, “Yes. I only open attachments from
people I know.” Wrong answer! If you think that attachments from people you know
are safe, then you’re precisely the person who should be reading this column.
The crazy people in this world who create computer viruses
figured out long ago that the best way to circulate viruses was to capitalize on
the trust people have in their friends. So they programmed their viruses to
search an infected computer for an address book and then e-mail the virus to all
the people listed. To encourage the recipient to open the attachment, they
included in the body of the message something like “thought you might be
interested in the attached file.” When one of the recipients carelessly opened
the attachment sent by a friend, the process repeated and the virus propagated
itself, often around the world, in no time at all.
Here’s another way viruses circulate: The programmer of the
Klez virus tricked people into infecting their computers by sending out e-mails
warning of the Klez virus! It described in gory detail what the virus could do
to a computer. Attached to the e-mail was a program guaranteed to inoculate the
computer against this virus along with a plea to forward the e-mail to friends
in order that they might protect their PCs in turn. Gullible people by the
millions opened this attachment in hopes of safeguarding their machine—only to
discover that the attachment itself was the virus! Even people with up-to-date
anti-virus software weren’t immune.
So if you can’t identify a potential virus-infected e-mail
attachment by identifying who sent it to you, what can you do? Easy. For the
most part, a file can only be infected with a computer virus if its
extension—the last three characters of the filename following the last period—is
of a certain type. Therefore, you can easily reduce the chances of an attachment
infecting your machine by simply not opening it if its extension is one of the
following: .EXE, .COM, .VBS, .WSH, .PIF, .SCR, .LNK, .BAT, .DLL, .SHS.
Remember you can’t go by the sender of the message. Never open
an e-mail attachment that ends in one of these extensions, regardless of who
sent the e-mail and regardless of what the e-mail message says or claims.
Here are some examples of virus-infected files. Note that they
all end in one of the extensions listed above: readme.com, this
websiteisgreat.htm.vbs, nice-picture.jpg.bat, click-this.exe, greatjoke.scr.
Also, be cautious of files that end in the extension .ZIP. These zip files
contain compressed versions of other files. While a zip file itself can’t
contain a virus, a file compressed within the zip file can. So be sure to check
the names of the files contained within an attached zip file to be certain they
don’t end in one of these dangerous extensions.
This is Larry Schneider, logging off.
