CHAPTER 1. COMPUTER
VIRUSES AND MALWARE
The risks of computer virus infection and data damage or theft through other
malicious software has grown as the number of computer users increases,
together with the number of opportunities for data exchange between them via e-
mail and the Internet.
It would be useful to learn about the types of malware and how they function in
order to understand the threats that they pose to your data.
The following classes of malware can be defined according to their specific
manifestations:
•
Worms
– malware belonging to this category copies itself to network re-
sources. The name of this class comes from the ability of worms to “crawl”
from one computer to another through networks, e-mail and other infor-
mational channels. This feature enables worms to spread extremely
quickly.
They penetrate computer memory, calculate network addresses of other
computers and send copies of themselves to those addresses. Apart from
network addresses, they frequently use the data from e-mail client ad-
dress books. Programs of this class may sometimes have work files on
system disks, but they might not use any resources on a computer at all
(except for RAM).
•
Viruses
– programs that infect other programs by embedding their own
code into the latter in order to gain control when infected files are
launched. This simplified definition lets us identify the main action that a
virus performs –
infection
. Viruses spread somewhat slower than worms.
•
Trojans
– programs that perform actions which the user has not author-
ized; for example, depending upon certain conditions, they may destroy
the information recorded on disks, cause the system to “hang”, steal con-
fidential data, etc. Programs belonging to this class are not viruses in the
traditional understanding of the term; Trojans cannot penetrate target
computers independently and therefore they are passed off by intruders
as “useful” software.
•
Damage caused by Trojan software may exceed the losses from tradi-
tional virus attacks by tenfold, since the consequences of viruses may be
minimized using an adequate backup system.
In recent times, worms have become the most wide-spread type of malware
corrupting computer data. Then viruses and Trojans follow, judging by the
