Types of Viruses

1. Logic Bombs: The logic bombs are the simplest example of malicious code. They are rarely stand-alone programs. Most often, they are a piece of code embedded in a larger program. The embedding is usually done by the programmer (or one of the programmers) of the larger program.”

2. Trojan Horses: A Trojan Horse is a program which performs (or claims to perform) something useful, while in the same time intentionally performs, unknowingly to the user, some kind of destructive function. This destructive function is usually called a payload.” Subtypes of Trojan Horses are: Regular Trojan Horses (available from BBS), Trapdoors, Droppers, Injectors and Germs.

3. Droppers: A dropper is a special kind of Trojan Horse, the payload of which is to install a virus on the system under attack. The installation is performed on one or several infectable objects on the targeted system.

4. Injectors: An injector is a program very similar to a dropper, except that it installs a virus not on a program but in memory.

5. Germs: A germ is a program produced by assembling or compiling the original source code (or a good disassembly) of a virus or of an infected program. The germ cannot be obtained via a natural infection process. Sometimes the germs are called first generation viruses.

6. Computer Virus: A computer virus is a computer program which is able to replicate itself by attaching itself in some way to other computer programs. … (The) two main properties of the computer viruses (are) —merely that a virus is able to replicate itself and that it does it by always attaching itself in some way to another, innocent program. This process of virus replication and attaching to another program is called infection. The other program, i.e., the program that is infected by the virus is usually called a host or a victim program.

7. Worms: Programs which are able to replicate themselves (usually across computer networks) as stand-alone programs (or sets of programs) and which do not depend on the existence of a host program are called computer worms.” Subtypes of “Worms”: Chain Letters, Host Computer Worms (with a special form called Rabbits), and Network Worms (with its special form “Octopus” where the central segment manages the worm`s behaviour on the network).