Computer viruses are similar to biological viruses in the way they multiply in number and in the way they need a host to survive. However, in both scenarios there must be a cause, such a weak immune system or an expired anti-virus program, in order for the virus to penetrate and spread. Having a reliable anti-virus program is the best solution. In computing terminology, a ‘malicious code’ is a term used for computer viruses and programs designed to cause damage to computers. Other types of destructive PC worms are known as viruses.

Falling under the category of parasitic viruses, a program or file infector attempts to infect the files with extension code like .exe, .com, .drv, .dil, .bin, .ovl, and .sys. It gets activate along with the execution of executable file containing virus. The virus then loads itself into memory and replicates itself to other executable files when these files are opened or run.

The File Infector virus can destroy the content contained in files and cause irreversible damage to them. Some file viruses have also operated as email worm and Trojan horse. The best way to disinfect files infected by the file virus is to delete them and restore from back up.

Similarly Multi-Partite Virus they are hybrids and behave in the same way as other computer viruses do. As the name signifies, they are sometimes more than one type.

When talking about Macro Viruses, we refer to viruses which infect macro of other applications such as Microsoft Word, Microsoft Excel. The viruses are written in a macro language and use it to distribute themselves. Macro viruses will run automatically when user open document. Usually this type of virus cause harmless to your computer, but instead they are annoying by automatically inserting undesired texts or symbols.

Example of Macro Virus: WM. Concept, it was introduced in 1995 the first macro virus that spread through Microsoft Word. And another popular one is Melissa that is first found in 1999, it also can spread through MS Word, Excel and Outlook.

Logic Bomb Viruses or sometime know as Time Bomb is small piece of malicious code or program which have ability to insert itself to other programs or system and perform specific action when the conditions are met (most Logic Bomb developers use date as conditions). The Logic Bomb does nothing until pre-programmed date is reached. Logic Bomb can perform any malicious things based on pre-programmed within it such as deleting file or displaying unwanted message or lock program and so on.

Boot sector Viruses are the type of viruses that has ability to hide in boot sector. The viruses will load into memory when there is booting system and trying to read from hard disk. Boot sector viruses are more spread since old time when floppy disk was popular. But now we hardly seen them since many of them only can spread through floppy disk

Companion Viruses is another kind of viruses. When user computer infect by this sort of viruses, it will create another type file from an existing file in same directory such as creating file.com from file.exe in the same folder, some companion viruses create file.exe from any folder.