DIFFERENT TYPES OF COMPUTER VIRUSES

Computer viruses come in a variety of types. Breaking them into categories is not easy as many viruses have multiple characteristics and so would fall into multiple categories.

A computer virus is a program designed to harm or cause harm on an infected computer. Its spreads through e-mail attachments, portable devices, websites containing malicious scripts and file downloads. A computer virus attaches itself to the host files and always activate whenever you open the infected files. The virus can replicate itself and then infect the other files on your computer causing more damage. Below is a list of different types of computer viruses and what they do.

The Types of Viruses

Virus Type	What It Does	How Affects Our PC
Program or File Virus	Infects executables (other programs, with affixes such as EXE, BIN, COM, SYS)	Destroys or alters programs and data.
Boot sector Virus	Infects boot sectors on hard and floppy disks	Destroys or alters programs and data.
Multipartite Virus	A hybrid of a program and boot sector virus	Destroys or alters programs and data.
Macro Virus	Triggers on a command in  Microsoft Office	Commonly affects Word & Excel
Stealth Virus	Uses various tactics to avoid detection.	Destroys or alters programs and data.
Polymorphic Virus	Uses encryption to foil detection, so that it appears differently in each infection.	Destroys or alters programs and data.

Macro Viruses

These viruses infect the files created using some applications or programs that contain macros such as doc, pps, xls and mdb. They automatically infect the files with macros and also templates and documents that are contained in the file. They hide in documents shared through e-mail and networks.

Macro viruses include:

• Relax
• bablas
• Melissa.A
• 097M/Y2K

Memory Resident Viruses

They usually fix themselves inside the computer memory. They get activated every time the OS runs and end up infecting other opened files. They hide in RAM.

Memory Resident Viruses Include:

• CMJ
• meve
• randex
• mrklunky

Overwrite Viruses

These types of viruses delete any information in a file they infect, leaving them partially or completely useless once they are infected. Once in the computer, they replaces all the file content but the file size doesn’t change.

Overwrite Viruses Include:

• Trj.Reboot
• way
• trivial.88.D

Direct Action Viruses

These viruses mainly replicate or take action once they are executed. When a certain condition is met, the viruses will act by infecting the files in the directory or the folder specified in the AUTOEXEC.BAT. The viruses are generally found in the hard disk’s root directory, but they keep on changing location.

Direct Action Viruses Include:

• Vienna virus

Directory Virus

Also known as cluster virus or file system virus. They infect the computer’s directory by changing the path indicating file location. They are usually located in the disk but affect the entire directory.

Directory Viruses Include:

• dir-2 virus

Web Scripting Virus

Most web pages include some complex codes in order to create an interactive and interesting content. Such a code is often exploited to cause certain undesirable actions. They mostly originate from the infected web pages or browsers.

Web Scripting Viruses Include:

• JS.Fortnight – a virus that spreads via malicious emails.

Multipartite Virus

These type of viruses spread in many different ways. Their actions vary depending on the OS installed and presence of certain files. They tend to hide in the computer’s memory but do not infect the hard disk.

Multipartite Viruses Include:

• flip
• invader
• tequila

FAT Viruses

These lardy viruses attack the file allocation table (FAT) which is the disc part used to store every information about the available space, location of files, unusable space etc.

FAT Viruses Include:

• the link virus

Companion Viruses

These types of viruses infect files just like the direct action and the resident types. Once inside the computer, they ‘accompany’ other existing files.

Companion Viruses Include:

• Asimov.1539
• stator and terrax.1069

Polymorphic Virus

They encode or encrypt themselves in a different way every time they infect your computer. They use different encryption and algorithms. This makes it difficult for the antivirus software to locate them using signature or string searches (since they are very different in each encryption).

Polymorphic Viruses Include:

• Marburg
• tuareg
• Satan bug
• elkern

Worm

This program is very similar to a virus and has the ability to self-replicate leading to negative effects on your computer.

Worm Viruses Include:

• lovgate.F
• sobig.D
• trile. C
• PSWBugbear.B
• Mapson

Trojans

Trojans can illegally trace important login details of users online. For example E-Banking is very common among users, therefore, vulnerability of tracing your login details whenever your PC is working without any strong powerful antivirus installed.

Email Virus

This is a virus spread via an email. Such a virus will hide in an email and when the recipient opens the mail.

Browser Hijacker

This virus can spread in many different ways including a voluntary download. If infects certain browser functions especially in form of re-directing the user automatically to certain sites. A good example is

Browser Hijackers Include:

• the cool web search

Boot Infectors

They include the boot sector plus master boot record types. All the viral codes can be separate location; however they infect the hard disks or the floppy.

Boot Infectors Include:

• the brain virus -it is the very first wild virus to be created.

From what we have seen, the many types of computer viruses and their effects are very harmful and can completely damage your system. Always make sure your system is up to date. Also install antivirus software. The antivirus program protects your computer and the personal information in it.