Computer Virus

What is Computer Virus? A computer virus is a human written computer program or a piece of code that can replicate itself and travel from one computer to another infecting them. The term "virus" is also commonly, but erroneously, used to refer to other types of malware, including adware and spyware programs that do not have ability to replicate itself. Malware includes computer viruses, computer worms, ransomware, trojan horses, keyloggers, most rootkits, spyware, dishonest adware, malicious BHOs and other malicious software.

The majority of active malware threats are usually trojans or worms rather than viruses. Malware such as trojan horses and worms is sometimes confused with viruses, which are technically different: a worm can exploit security vulnerabilities to spread itself automatically to other computers through networks, while a trojan horse is a program that appears harmless at first but hides malicious functions. Worms and trojan horses, like viruses, may harm a computer system's data or performance. Some viruses and other malware have symptoms noticeable to the computer user, but many are surreptitious or simply do nothing to call attention to themselves. Some viruses do nothing beyond reproducing themselves.

Some types of computer viruses

• Viruses: A virus is a small piece of software that can attach itself to a program such as a spreadsheet program. Each time the spreadsheet program runs, the virus runs, too, and it has the chance to reproduce by attaching to other programs.
• E-mail viruses: An e-mail virus travels as an attachment to e-mail messages, and usually replicates itself by automatically mailing itself to dozens of other people in the victim's e-mail address book.
• Trojan horses: A Trojan horse is also simply a computer program. The program claims to do one thing (it may claim to be a game) but instead does damage when you run it (it may erase your hard disk). Trojan horses have no way to replicate automatically.
• Worms: A worm is a small piece of software that uses computer networks and security holes to replicate itself. A copy of the worm scans the network for another machine that has a specific security hole. It copies itself to the new machine using the security hole, and then starts replicating from there, as well.