- Parasitic Virus:- his is the most common form of virus. Such a virus attaches itself to executable files and keeps replicating, Whenever the infected file is executed, the virus looks for other executable files to attach itself and spread.
- Memory-resident Virus:- This type of virus first attaches itself to an area of the main memory and then infects every executable program that is executed.
- Boot sector Virus:- This type of virus infects the master boot record of the disk and spreads on the disk when the operating system starts booting the computer.
- Stealth Virus:- This virus has intelligence built in, which prevents anti-virus software programs from detecting it.
- Polymorphic Virus:- A virus that keeps changing its identity 0n every execution, making it very difficult to detect it.
- Metamorphic Virus:- In addition to changing its signature like a polymorphic virus, this type of virus keeps rewriting itself every time, making its detection even harder. There is another popular category of viruses, called the macro virus. This virus affects specific application software; such as Microsoft Word or Microsoft Excel. They affect the documents created by users, and spread quite easily since such documents are very commonly exchanged over email. There is a feature called macro in these application software programs, which allows users to write small, useful, utility programs within the documents. Viruses attack these macros, and hence the name macro virus.
