How do trojan horse spread out?

A computer system infection is a kind of harmful code or program that, when carried out, duplicates itself by modifying other computer system programs and inserting its own code. When this duplication is successful, the affected locations are then said to be infected with a virus.

Infections frequently spread out by producing a copy of themselves on a user's computer without the user's knowledge or approval.  https://westpennjournal.com/?p=381 In a lot of cases, viruses will be spread by email accessories or by files shared on peer-to-peer networks. Once an infection has contaminated a computer system, it can infect other computer systems on the exact same network.

Some infections are set to spread themselves in a manner that could cause major damage to a computer system. An infection might erase files, fill a difficult drive with ineffective data, or corrupt system files. In many cases, a virus may even display a message or image that is designed to terrify the user.

https://cleardex.io/?p=852 The majority of viruses are reasonably harmless, and just cause small annoyance to the user. However, some viruses can be very harmful, and can trigger widespread damage to computer systems.