# Section 04: Virus and Worms Concepts ## Viruses and Worms Virus > A computer virus is a type of computer program that, when executed, replicates itself by modifying other computer programs and inserting its own code. Polymorphic virus > A polymorphic virus is a harmful, destructive or intrusive type of malware that can change or "morph," making it difficult to detect with antimalware programs. Metamorphic virus > Metamorphic code is code that when run outputs a logically equivalent version of its own code under some interpretation. This is similar to a quine, except that a quine's source code is exactly equivalent to its own output. Metamorphic code also usually outputs machine code and not its own source code. Macro virus > In computing terminology, a macro virus is a virus that is written in a macro language: a programming language which is embedded inside a software application (e.g., word processors and spreadsheet applications). Boot sector virus > A boot sector virus is a type of malware that infects a system's boot partition or the Master Boot Record (MBR) of a hard disk. During startup and before security software can be executed, the virus executes malicious code. Logic bomb > A logic bomb is a piece of code intentionally inserted into a software system that will set off a malicious function when specified conditions are met. For example, a programmer may hide a piece of code that starts deleting files (such as a salary database trigger), should they ever be terminated from the company. Virus hoax > A computer virus hoax is a message warning the recipients of a non-existent computer virus threat. The message is usually a chain e-mail that tells the recipients to forward it to everyone they know, but it can also be in the form of a pop-up window. Worm > A computer worm is a standalone malware computer program that replicates itself in order to spread to other computers. It often uses a computer network to spread itself, relying on security failures on the target computer to access it. Links * * * * *