A virus is a type of malicious software that is able to replicate itself and spread by inserting copies of its code into other executable programs without the user's consent or knowledge. It consists of a small set of instructions that allow it to reproduce and spread throughout an infected computer. There are two phases for a virus - an inert phase when it resides on a storage device, and an active phase when it is loaded into memory and can begin carrying out its programmed actions. Trojans are another type of malware that masquerade as legitimate programs to trick users into running them and allowing the malicious code to execute. In the past, virus programmers would exchange source code through websites called VX sites to share new programming techniques.

1. Virus