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MALWARE

Malware is a trouble-causing program. It may be a virus, worm, trojan horse or spyware. Malwares
not only intercept the normal working of a computer but also steal important information.

Classification of Malicious Software

1. Virus : Computer viruses are programs that are written with the intention of damaging data on a
computer. These viruses multiply and spread from one computer to another through CDs,
pendrives, the internet (while downloading files) etc.
2. Worm : A worm is a program very similar to a virus. It has the ability to self-replicate and can

lead to negative effects on your system. But they can be detected and eliminated by an antivirus
software. These are generally spread through e-mails and networks. They don’t infect files or
damage them but they replicate so fast that the entire network may collapse.

Example : Melissa, My doom, My life, etc.
3. Trojan Horse : It is a simple program that pretends to be a useful application, where as it always
do something destructive– mostly it damages a computer, like erasing a disk. It is not self-

replicating. It can spread only when it is copied to another system.
4. Spyware : Spyware is a type of malware that covertly gathers user’s information through the

user’s internet connection without his or her knowledge usually for advertising purpose. Spyware
applications are typically bundled as a hidden component of freeware or shareware programs that
can be downloaded from the Internet. Spyware programs secretly monitor the users’ computing.
They can collect various types of personal information, such as internet surfing habits, visited web
pages and transmits that information in the background to someone else. Sometimes they also
change computer’s setting that result in slow connection speed and wrong functionality of other
programs. Spyware can also collect information about e-mail addresses, passwords, and even credit
card numbers.

TYPES OF COMPUTER VIRUSES

There are various types of computer viruses classified in terms of techniques, origin and the types
of files attached as well as the places they hide. While a few viruses are harmless, most are
malicious and cause widespread damage and destroy files.

Viruses can be classified by their infection targets into the following types :

1. Boot Sector Viruses : The boot sector is the first software loaded onto your computer. A boot
sector virus infects computers by modifying the contents of the boot sector program. It replaces the
legitimate contents with its own infected version.

Examples : Disk Killer, Stoned Virus etc.
2. Program File Viruses : These viruses infect executable files, programs, such as those with

extension, like .com, .exe, .ovl, .drv, .sys etc. These programs get loaded in the computer memory
during execution. The virus becomes active in the computer memory by replicating itself and
infecting files on the disk.
Examples : Sunday, Cascade etc.

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