Information Technology Reference
In-Depth Information
what, modern word processing systems and spreadsheets often al
low users to write small programs (sometimes called
macros
) for use
within a document. One simple part of a spreadsheet, for example,
could compute the sum of the numbers in a row. More complex in
structions could tell the wordprocessing package or spreadsheet to
access files, change data, send email, or erase materials. A virus is a
set of such instructions within a document that instructs a word
processor, spreadsheet, or other program to carry out unwanted ac
tivities when a document is opened.
Because you are running the program (word processor or
spreadsheet) on your computer, the program has the capability to
access your files. With that access, the virus embedded in an attach
ment could cause your word processor or spreadsheet to change
your files, access your lists of email addresses, or send email. Like
any program, once a virus is launched, it is difficult to monitor.
Because you have little control over what an unknown attachment
program might do, it is strongly suggested that you
not
open email
attachments unless you know who they are from and what will
happen.
On another front, when a diskette is inserted into a machine, the
computer reads some initial data to learn about the type of material
present. If this initial information is altered, the computer could be
instructed to change its programs, data, or mode of operations. In
this way, disk viruses can cause just as much damage as attach
ments, and you should be equally careful in working with email at
tachments and potentially infected disks.
Worms
typically enter machines over network communication
channels that we trust to be reliable. A worm takes advantage of
weaknesses in one system to transmit itself to other machines, where
the program may be duplicated and retransmitted. The scope and
seriousness of its effects depend upon its design, as well as particu
lar networks and machines.
In many cases, both worms and viruses are designed to perform
some unusual or clandestine operation, and then they tell the com
puter to make additional copies of themselves. These additional
copies may then be transmitted and run on either your computer or
other machines to cause further deterioration of a system or net
work. Sometimes this duplication process has the potential to de
stroy a great deal of data or to bring normal operations to a halt. As
in medicine, a single virus program (or cell) may be relatively harm
less by itself, but as it reproduces (producing more copies of itself),
the result can overwhelm the health of a system.
