Taxonomy of malicious programs
Trap doors
Trap doors are a secret entry point in to a program that allows some one that aware of the trap door to gain access without going through the usual security access procedures. Trap doors become threats when they are used by unscrupulous programmers to fain unauthorized access.
Logic Bombs
Just like a real bomb, a logic bomb will lie dormant until triggered by some event. The trigger can be a specific date, the number of times executed, a random number, or even a specific event such as deletion of an employee's payroll record. When the logic bomb is triggered it will usually do something unpleasant. This can range from changing a random byte of data somewhere on your disk to making the entire disk unreadable. The changing of random data on disk may be the most insidious attack since it would do a lot of damage before it would be detected.
Trojans
These are named after the Trojan horse which delivered soldiers into the city of
Viruses
Here's our definition:
“A virus is a program which reproduces its own code by attaching itself to other programs in such a way that the virus code is executed when the infected program is executed.”
You could also say that the virus must do this without the permission or knowledge of the user
A worm is a self-reproducing program which does not infect other programs as a virus will, but instead creates copies of itself, which create even more copies. These are usually seen on networks and on multi-processing operating systems, where the worm will create copies of itself which are also executed. Each new copy will create more copies quickly clogging the system. The so called Morris ARPANET/INTERNET "virus" was actually a worm. It created copies of itself through the ARPA network, eventually bringing the network to its knees. It did not infect other programs as a virus would, but simply kept creating copies of itself which would then execute and try to spread to other machines.
Zombie
A zombie is a program that secretly takes over another internet –attached computer and then uses that computer to launch that are difficult to trace to the zombie’s creator .Zombies are used in denial of services attacks, typically against targeted websites.
