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What is a virus - computer

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What is a virus - computer

What is a VIRUS

Virus (computer), self-duplicating computer program that interferes

with a computer's hardware or operating system (the basic software

that runs the computer). Viruses are designed to duplicate or

replicate themselves and to avoid detection. Like any other computer

program, a virus must be executed for it to function-that is, it must

be located in the computer's memory, and the computer must then follow

the virus's instructions. These instructions are called the payload of

the virus. The payload may disrupt or change data files, display an

irrelevant or unwanted message, or cause the operating system to

malfunction.

Computer viruses activate when the instructions-or executable

code-that run programs are opened. Once a virus is active, it may

replicate by various means and tries to infect the computer's files or

the operating system. For example, it may copy parts of itself to

floppy disks, to the computer's hard drive, into legitimate computer

programs, or it may attach itself to e-mail messages and spread across

computer networks by infecting other shared drives. Infection is much

more frequent in PCs than in professional mainframe systems because

programs on PCs are exchanged primarily by means of floppy disks,

e-mail, or over unregulated computer networks.

Viruses operate, replicate, and deliver their payloads only when they

are run. Therefore, if a computer is simply attached to an infected

computer network or downloading an infected program, it will not

necessarily become infected. Typically a computer user is not likely

to knowingly run potentially harmful computer code. However, viruses

often trick the computer's operating system or the computer user into

running the viral program.

Some viruses have the ability to attach themselves to otherwise

legitimate programs. This attachment may occur when the legitimate

program is created, opened, or modified. When that program is run, so

is the virus. Viruses can also reside on portions of the hard disk or

floppy disk that load and run the operating system when the computer

is started, and such viruses thereby are run automatically. In

computer networks, some viruses hide in the software that allows the

user to log on (gain access to)

Types of VIRUS

There are five categories of viruses: parasitic or file viruses,

bootstrap sector, multi-partite, macro, and script viruses.

Parasitic or file viruses infect executable files or programs in the

computer. These files are often identified by the extension .exe in

the name of the computer file. File viruses leave the contents of the

host program unchanged but attach to the host in such a way that the

virus code is run first. These viruses can be either direct-action or

resident. A direct-action virus selects one or more programs to infect
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