A virus is type of malware that produces multiple copies of itself by attaching to another program or file. Furthermore, it spreads from one computer to another by embedding copies of itself into files. However, the virus cannot transfer from one host to another by itself. I will rather require human or program intervention to propagate. It is commonly spread via email attachments, removable media, network, malicious links and so on.
A virus has two modules namely insertion code and payload. The insertion code helps the virus to inject a copy of itself into one or more programs of the target. The payload part is the code that actually performs the malicious action associated with the virus. Moreover, the payload replicates itself onto an executable file and attacks a system. In short, it will employ infection phase and attack phase to unleash its nefarious intent.
The following are the major types of virus:
- Multipartite Virus: a virus that infects targets and spreads via multiple ways such as DOS, BIOS boot sector and so on virus codes.
- Macro Virus: a virus written with the same macro programming language applied in software programs, which is common virus in Microsoft Excel and Word programs.
- Polymeric Virus: a virus that affects data types and functions of programs. A polymorphic virus is a self-encrypted virus developed to avoid detection through common scanners.
- Stealth Virus: a virus type that employs different techniques to avoid detection by antimalware software.