Types of Computer Viruses

Computer Virus is a program written that can attaches to file. When the infected file is opened, the virus infects other files on the system, and also spreads to other systems with the help of infected files. Viruses damage the system by deleting files on the system, increasing the file sizes, or automatically formatting the system.

1. Boot Viruses

The boot sector viruses copies the virus code in the boot sector of the disk, this ensures that the virus is always executed and loaded in the memory when the sytem starts. Once in the memory , the virus infects other files and floppy diks inserted in the drive, and spread it to other systems. For example, the virus Tequila onfects all the EXE files on the system and also infects the Master Boot record of the hard disk.

2. Polymorphic Viruses

A person can keeps on changing the way he looks to disguise himself this makes it difficult to trace a person. Similarly, polymorphic viruses are coded in such a way that they infect a system and change their signature before infecting the next system. Thus, the Antivirus software finds it difficult to identify this virus , as it looks different after every infection.

3. Macro Viruses

Macros are blocks of code written to automate frequently performed tasks and embedded in a program file such as Word document or an Excel worksheet. When a Macro having the virus code is executed, it infects the files on the system.

4. Worms

Worms are programs that replicate and spread to other systems. A Worm resides in the system memory and spreads without attaching itself to a file. They may cause damage to the system such as deleting files from the system and may also the system may slow down. For example , the worm Mwlissa attaches itself to an email and sends the email to all the contacts specified in the users address book, it also clogs email servers.

5. Trojans

Trojan is a program file that claims to do something but it actually does something that is not required. For Example, a Trojan may pose a computer game but when it is executed it may delete files from your sytem or email the passwords stored in your system to the Trojanwriters email address.

6. Spywares

Spyware stores personal information and surfing habits of the user sends them to its web site without informing the user. Many spywares get installed as a free download while installing an application. It does not harm the computer as a virus does but is used to get user information for monetary gains.