What is Computer Virus..??

A computer virus is a computer program (a piece of code) that can replicate itself. It loaded onto your computer without your knowledge and run against your wishes. The term”Virus “is commonly. But erroneously, used to refer to other types of malware .All computer viruses are human-made programs. A simple virus that can make a copy of it (replicate itself) over and over again is relatively easy to produce. This type of virus is known as Memory Resident Viruses Even such simple virus is very dangerous because it will quickly use all available memory and bring your computer to a halt
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There are so many types of viruses and malwares and it’s very difficult to define them all in detail, so here I’m going to explain some of these in brief:-

1.  Trojan horse:A Trojan is a malicious program, which infect you computer system in a silent way. Trojans comes on the backs of other programs and are installed on a system without the User’s knowledge. Trojans are malicious pieces of code used to install hacking software on a target system and aid the Hacker in gaining and retaining access to that system. There are so many different type of Trojan, some of these are:-

i)       Remote Administration Trojans

ii)    Data Stealing Trojans

iii)  Security Disabler Trojan

iv)  Control changer Trojan

Some Famous Trojan are:

i)      Beast

ii)    Back orifice

iii) Net Bus

iv) Pro rat

v)   Girl Friend  

vi) Sub seven etc.

2.  Boot sector Virus: A virus which attaches itself to system boot Files that is read by the computer at the time of booting. These are normally spread by floppy disks.

3.  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.

4.  Worms: A worm is a program that makes and facilitates the distribution of copies of itself.

E.g. from one disk drive to another, or by copying itself using email. The worm may do damage and compromise the security of the computer. It may arrive via exploitation of system vulnerability or by clicking on an infected e-mail. The most common source of Worms are fake email or email attachments

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

6.  Rootkit Virus: A rootkit virus is an undetectable virus which attempts to allow someone to gain control of a computer system. The term rootkit comes from the linux administrator root user. These viruses are usually installed by Trojans and are normally disguised as operating system files.

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