B1) What are computer viruses (and why should I worry about them)?

According to Fred Cohen's well-known definition, a COMPUTER VIRUS is a
computer program that can infect other computer programs by modifying
them in such a way as to include a (possibly evolved) copy of itself.
Note that a program does not have to perform outright damage (such as
deleting or corrupting files) in order to to be called a "virus".
However, Cohen uses the terms within his definition (e.g. "program"
and "modify") a bit differently from the way most anti-virus
researchers use them, and classifies as viruses some things which most
of us would not consider viruses.

Many people use the term loosely to cover any sort of program that
tries to hide its (malicious) function and tries to spread onto as
many computers as possible.  (See the definition of "Trojan".)  Be
aware that what constitutes a "program" for a virus to infect may
include a lot more than is at first obvious - don't assume too much
about what a virus can or can't do!

These software "pranks" are very serious; they are spreading faster
than they are being stopped, and even the least harmful of viruses
could be fatal.  For example, a virus that stops your computer and
displays a message, in the context of a hospital life-support
computer, could be fatal.  Even those who created the viruses could
not stop them if they wanted to; it requires a concerted effort from
computer users to be "virus-aware", rather than the ignorance and
ambivalence that have allowed them to grow to such a problem.


.