TYPES OF VIRUS

TYPES OF VIRUS

There are thousands of viruses and several are discovered everyday. They have variations in the way they infect or the way they spread.

Some common categories of the viruses are:

Boot Sector Viruses
Boot sector viruses affect the hard disk.


This type of computer virus spreads by hiding itself in the boot sector of a hard disk or a floppy disk and infects the start-up instructions which are required to boot the system. Virus loads itself each time into memory on every boot sequence.

A boot sector virus overwrites the original boot record with the infected one. When the other disks are used the virus is transferred to their boot sectors also. These affect only the disks.

Polyboot and ANtiEXE are the example.

It doesn’t affect the contained files.



File Virus

File viruses attach themselves to the executable files, driver files or other files.They are activated when such files are run.
The virus spreads itself to other programs on the computer. Virus disturbs the relate files.

Randex is a file virus.



Network virus

Network virus affects the systems by searching the network for them.They quickly spread across a Local Area Network. Then they spread over the Internet.They spread by using the shared resources such as shared drives and folders.
Nimda is a network virus.


E-mail virus

E-mail virus spread through the contacts.These contacts are available in the host’s email address book.
Any recipient opens the attachment of an infected mail. They spread again to a new host’s address book contacts.
Heart is the name of an e-mail virus.



Program viruses

These viruses will infect only executable files like .BIN, .COM,.EXE,.OVL,.DRV AND .SYS.Once executed these programs load into memory along with the virus contained within them. Once in the memory, the scenario repeats the virus is free to act and infect other files or simply deliver its payload.

These viruses are friendlier than boot viruses and can be removed a lot easier.


Multipartite viruses

These computer viruses are hybirds, derived from boot viruses and program viruses.They infect executable files, just like the program viruses but once the executable is executed, it infects the master boot records.The scenario is similar to the boot viruses’ one. once you boot your operating system the virus is loaded into the memory from where it is free to infect other programs and replicate itself, ultimately delivering the payload.



Stealth viruses

These viruses are specialized in avoiding detection and will use a number of techniques to do so.A stealth virus is one that conceals the changes it makes.It does this by taking control of system functions that interpret files or system sectors.

Stealth virus can falsely show any anti-virus software that a certain file is uninfected.


Polymorphic Viruses

These viruses will always change their source code from one infection to another.Each infection is different and this makes detection very hard.
Detection is possible depending on the antivirus.


Macro viruses

This virus is relatively new and it infects macros within a template or document.When you open a word processing document, it activates the virus.The virus infects the normal.dot template, which general file used by all the documents.
Whenever you open uninfected document by referring to the normal.dot file, it gets infected as well.This infected can only spread if infected documents are opened on another machine.