Computer Viruses

A virus is a parasitic program that infects another legitimate program, which is sometimes called the host. To infect the host program, the virus modifies the host so that it contains a copy of the virus. 

Boot sector viruses: A boot sector virus infects the boot record of a hard disk. The virus allows the actual boot sector data to be read as through a normal start-up were occurring.

Cluster viruses: If any program is run from the infected disk, the program causes the virus also to run . This technique creates the illusion that the virus has infected every program on the disk.

Worms: A worm is a program whose purpose is to duplicate itself.

Bombs: This type of virus hides on the user’s disk and waits for a specific event to occur before running.

Trojan Horses: A Trojan Horses is a malicious program that appears to be friendly. Because Trojan Horses do not make duplicates of themselves on the victim’s disk. They are not technically viruses.

Stealth Viruses: These viruses take up residence in the computer’s memory, making them hard to detect.

Micro Viruses: A macro virus is designed to infect a specific type of document file, such as Microsoft Word or Microsoft Excel files. These types of documents can include macros, which are small programs that execute commands.