8
Kaspersky Security 5.5 for Microsoft Exchange Server 2003
crawl from computer to computer, using networks, e-mail, and other data
channels. This feature gives many worms a rather high speed in spread-
ing themselves.
Worms penetrate a computer, calculate the network addresses of other
computers, and send a burst of self-made copies to these addresses. In
addition to network addresses, worms often utilize data from e-mail client
address books. Some of these malicious programs occasionally create
working files on system disks, but they can run without any system re-
sources at all (with the exception of RAM).
Viruses
Programs that infect other programs, adding their own code to them to
gain control of the infected files when they are opened. This simple defini-
tion explains the fundamental action performed by a virus –
infection
.
Trojans
Programs that carry out unauthorized actions on computers, such as de-
leting information on drives, making the system hang, stealing confidential
information, etc. These malicious programs are not viruses in the tradi-
tional sense of the term, since they do not infect other programs or data;
Trojans are not capable of independently penetrating computers. Their
users spread them under the guise of useful software. The damage that
they incur can exceed that done by traditional virus attacks by several
fold.
Recently, worms have become the most widespread type of malware, followed
by viruses and Trojans. Some malicious computer programs have characteristics
of two or even all three of the above categories.
Henceforth in the text of this Administrator’s Guide the term "virus" will
be used to refer collectively to viruses, Trojan Horses, and worms. A
particular type of malware will be mentioned only when it is required.
The following potentially dangerous types of malware have also become
widespread:
Adware
Program code included in software, unbeknownst to the user, designed to
display advertisements. Adware is usually built into software that is dis-
tributed for free. The advertisement is situated in the program interface.
These programs often also collect personal data on the user and send it
back to their developer, change browser settings (start page and search
pages, security levels, etc.) and also create traffic that the user cannot
control. All this can lead to breach of the security policy and to direct fi-
nancial losses.
