What are the effect and causes of Computer Viruses?

Computer virus: It is a computer program that replicates(multiplies) itself and destroys data, files, and programs of our computer system. Types of computer viruses

1. Boot sector: Infects master boot record (MBR) of our computer system. (Booting refers to starting of computer system)
2. File infector or program infector virus: Infect programs or executable files (.exe, .dmg, installer files)
3. Multipartite virus: Infects both boot sector and application programs.
4. Macro virus: Infects certain files created using macros such as MS Word, MS Excel, etc
5. Stealth virus: This can hide from being detected. It's hard to detect
6. Trojan horse: They do not replicate but are installed once then it starts malfunctioning.
7. WORM: Write Once Read Many