What is a computer virus? Computer virus definition - To put it in simple terms, computer virus is a small computer program that can replicate itself by attaching itself with applications and files. When the program executes, the virus also runs with it and replicate.
Once computer virus gets into a computer system it will cause problems depending on the threat level of a virus. Generally, computer virus is capable of damaging any kind of file and hampering the performance of a computer.
There are several types of computer viruses, commonly every malicious code such as Adware, Trojans, Spyware, Keylogger, Worm, Rootkit, Backdoor are called a virus. However, each type of dangerous code is different in behavior and damage level. For example, Trojans doesn’t replicate itself like a virus but it behaves like a legitimate program. When this program runs, it executes something a user doesn’t expect. Read more about types of computer viruses here.
“A computer program that is designed to replicate itself by copying itself into the other programs stored in a computer. It may be benign or have a negative effect, such as causing a program to operate incorrectly or corrupting a computer's memory.”
Source: American Heritage Dictionary
“Computer program designed to copy itself into other programs, with the intention of causing mischief or damage. A virus will usually execute when it is loaded into a computer's memory. On execution, it instructs its host program to copy the viral code into any number of other programs and files stored in the computer. The corrupted programs may continue to perform their intended functions while also executing the virus's instructions, thus further propagating it. The infection may transfer itself to other computers through storage devices, computer networks, and on-line systems. A harmless virus may simply cause a cryptic message to appear when the computer is turned on; a more damaging virus can destroy valuable data. Antivirus software may be used to detect and remove viruses from a computer, but the software must be updated frequently for protection against new viruses.”
Source: Britannica Concise Encyclopedia
“A program that enters a computer (usually without the knowledge of the operator). Some viruses are mild, and only cause messages to appear on the screen, but others are destructive and can wipe out the computer's memory or even cause more severe damage.Computer viruses spread from machine to machine on disks and through telephone lines.” Source: Dictionary of Cultural Literacy
“An insidious piece of computer code written to damage systems. Viruses can be hidden in executable program files posted online; micro viruses can infect documents created in Microsoft Word and Excel, both of which support executable Macros written in VBA code.” Source: Barron's Banking Dictionary
Computer virus can be removed by using quality anti-virus program. Not all anti-virus programs are capable of removing any kind of virus, so it will require your assessment to choose the best virus remover. Some of the popular anti-virus programs include Symatec/Northon, Kaspersky, MacAfee, AVG, Avira.