If you don??™t download any documents or applications from the Internet, if
you??™re not connected to a local network, if you have a firewalled connection
to the Internet, and the only type of software you install is off-the-shelf commercial
products, your odds of getting a virus are pretty much zero.
Viruses can only reside in certain types of files, including application (.exe
and .scr) files, document files made in applications that use macros (such as
Microsoft Word), Windows script files (.vbs), and some types of application
support files (.dll, .vbx, .vxd, etc.). And because ZIP files (described in
Chapter 2) can contain any of the aforementioned files, they??™re also susceptible.
Conventional wisdom holds that plain-text email messages,
text files (.txt), image files (.jpg, .gif, .bmp, etc.), video clips
(.mpg, .avi, etc.) and most other types of files are benign in
that they simply are not capable of being virus carriers. However,
things aren??™t always as they seem. Case in point: the
Bloodhound.Exploit.13 Trojan horse (discovered in 2004)
involved certain JPG files and a flaw in Internet Explorer
(and most other Microsoft products). The bug has since
been fixed, but it??™s not likely to be the last.
Actually, it is possible to embed small amounts of binary
data into image files, which means, theoretically, that an
image could contain a virus. However, such data would have
to be manually extracted before it could be executed; a virus
embedded in an image file would never be able to spontaneously
infect your system.
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