I know that you people are awaire about biological Viruses and their categorization. In the similar manner computer viruses are also categorise as par their behaviour toward Systems.
Their has been a continuous arm race between virus writers and the writers of anti virus software since Virus first appeared. As effective countermeasure has been developed for existing types of Viruses, New types has been developed.
Some popular types-
Parasitic Virus-> The traditional and still the most common form of Virus.A parasitic Virus attaches it self executable files and replicates when the infected program is executed, by finding other executable file to infect.
Memory-Resident Virus-> Lodges in main memory as part of a resident system program from that point on the Virus infects every program that executes.
Boot Sector Virus-> Infects a master boot record or boot record and spreads when a system is booted from the disk containing the Virus.
Stealth Virus-> A form of Virus explicitly designed to hide itself from detection by anti virus software.
Polymorphic Virus-> A Virus that mutates with every infection, making detection by the “signature” of the Virus in impossible.
Metamorphic Virus-> As with a Polymorphic Virus, a Metamorphic virus mutates with every infection.The difference is that a metamorphic Virus rewrites it self completely at each iteration.Metamorphic may change their behavior as well as their appearance.
