Virus Definition and Types of Viruses

Virus Definition

A computer virus is a program, piece of code, or programming script which runs without the user's knowledge and performs destructive or otherwise unwanted actions to a computer such as disabling or over-riding security features and making it vulnerable to other attacks. Computer viruses range from annoying and harmless, to extremely dangerous and destructive. Viruses normally replicate themselves by propagating throughout files. Viruses are normally spread by email, through a computer network, via floppy disks, or via the Internet.

Types Of Viruses

Trojan Horse: A trojan horse program has the appearance of having a useful and desired function. While it may advertise its activity after launching, this information is not apparent to the user beforehand. Secretly the program performs other, undesired functions. A Trojan Horse neither replicates nor copies itself, but causes damage or compromises the security of the computer. A Trojan Horse must be sent by someone or carried by another program and may arrive in the form of a joke program or software of some sort. The malicious functionality of a Trojan Horse may be anything undesirable for a computer user, including data destruction or compromising a system by providing a means for another computer to gain access, thus bypassing normal access controls.

Worm: A worm is a program that makes and facilitates the distribution of copies of itself; for example, from one disk drive to another, or by copying itself using email or another transport mechanism. The worm may do damage and compromise the security of the computer. It may arrive via exploitation of a system vulnerability or by clicking on an infected e-mail.

Bootsector Virus: A virus which attaches itself to the first part of the hard disk that is read by the computer upon bootup. These are normally spread by floppy disks.

Macro Virus: Macro viruses are viruses that use another application's macro programming language to distribute themselves. They infect documents such as MS Word or MS Excel and are typically spread to other similar documents.

Memory Resident Viruses: Memory Resident Viruses reside in a computers volitale memory (RAM). They are initiated from a virus which runs on the computer and they stay in memory after it's initiating program closes.

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