How do virus spread?

A virus is a type of destructive code or program that, when performed, reproduces itself by modifying other computer programs and inserting its own code. When this duplication succeeds, the impacted locations are then stated to be infected with a virus.

Viruses often spread by developing a copy of themselves on a user's computer without the user's knowledge or approval.  https://scarabnet.org/?p=2652 In many cases, viruses will be spread out by email attachments or by files shared on peer-to-peer networks. When an infection has contaminated a computer system, it can spread out to other computer systems on the same network.

Some viruses are set to spread themselves in a way that could cause serious damage to a computer system. For example, an infection might erase files, fill a hard disk drive with ineffective information, or corrupt system files. Sometimes, a virus may even show a message or image that is designed to terrify the user.

Many infections are fairly harmless, and just trigger small inconvenience to the user. However, some viruses can be extremely harmful, and can trigger widespread damage to computer system systems.