A virus can only spread from one computer to another when its host is taken to the uninfected computer, for instance by a user sending it over a network or the Internet, or by carrying it on a removable medium such as a floppy disk, CD, or USB drive. Meanwhile viruses can spread to other computers by infecting files on a network file system or a file system that is accessed by another computer. Viruses are sometimes confused with computer worms and Trojan horses.
A computer worm is a self-replicating computer program. A worm can spread itself to other computers without needing to be transferred as part of a host. It uses a network to send copies of itself to other nodes (computer terminals on the network) and it may do so without any user intervention. Unlike a virus, it does not need to attach itself to an existing program. Worms almost always cause harm to the network, if only by consuming bandwidth, whereas viruses almost always corrupt or modify files on a targeted computer
Trojan horse is a file that appears harmless until executed. a Trojan horse, is a piece of software which appears to perform a certain action but in fact performs another such as a computer virus. Contrary to popular belief, this action, usually encoded in a hidden payload, may or may not be actually malicious, but Trojan horses are notorious today for their use in the installation of backdoor programs. The term is derived from the classical story of the Trojan Horse.
Simply put, a Trojan horse is not a computer virus in most cases. Unlike such malware, it does not propagate by self-replication but relies heavily on the exploitation of an end-user (see Social engineering). It is instead a categorical attribute which can encompass many different forms of codes. Therefore, a computer worm or virus may be a Trojan horse.
Many viruses are programmed to damage the computer by damaging programs, deleting files, or reformatting the hard disk. Others are not designed to do any damage, but simply replicate themselves and perhaps make their presence known by presenting text, video, or audio messages.
Even these benign viruses can create problems for the computer user. They typically take up computer memory used by legitimate programs. As a result, they often cause erratic behavior and can result in system crashes. In addition, many viruses are bug-ridden, and these bugs may lead to system crashes and data loss.
Due to the complexity of viruses, it is extremely difficult even for an expert, to remove viruses form computers without the use of specific tools and antivirus software, because some viruses are designed to reinstall themselves after they have been detected and removed.
Antivirus software is a term used to describe a computer program that attempts to identify, neutralize or eliminate malicious software. Fortunately, there are many low cost antivirus software programs that if continuously updated can help permanently remove and prevent unwanted software form your PC.
Most Popular Anti Virus SoftwareBelow is a list of the Most popular Anti virus programs, the first two are completely free.
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Other anti virus protections programs include the following
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