Computer worms are also known as Network Mobile Code, or a virus-like bit of code that can replicate itself over a network, infecting adjacent computers.

A computer worm is a standalone malware computer program that replicates itself in order to spread to other computers. Often, it uses a computer network to spread itself, relying on security failures on the target computer to access it. Unlike a computer virus, it does not need to attach itself to an existing program. Worms almost always cause at least some harm to the network, even if only by consuming bandwidth, whereas viruses almost always corrupt or modify files on a targeted computer.

A notable example is the SQL Slammer computer worm that spread globally in ten minutes on January 25, 2003. I myself came to work that day as a software tester and found all my SQL servers infected and actively trying to infect other computers on the test network.

A patch had been released a year prior by Microsoft and if systems were not patched and exposed to a 376 byte UDP packet from an infected host then system would become compromised.

Ordinarily, infected computers are not to be trusted and must be rebuilt from scratch but the vulnerability could be mitigated by replacing a single vulnerable dll called sqlsort.dll.

Replacing that with the patched version completely disabled the worm which really illustrates to us the importance of actively patching our systems against such network mobile code.

The following answers are incorrect:

- Rootkit: Sorry, this isn't correct because a rootkit isn't ordinarily classified as network mobile code like a worm is. This isn't to say that a rootkit couldn't be included in a worm, just that a rootkit isn't usually classified like a worm. A rootkit is a stealthy type of software, typically malicious, designed to hide the existence of certain processes or programs from normal methods of detection and enable continued privileged access to a computer. The term rootkit is a concatenation of "root" (the traditional name of the privileged account on Unix operating systems) and the word "kit" (which refers to the software components that implement the tool). The term "rootkit" has negative connotations through its association with malware.

- Adware: Incorrect answer. Sorry but adware isn't usually classified as a worm. Adware, or advertising-supported software, is any software package which automatically renders advertisements in order to generate revenue for its author. The advertisements may be in the user interface of the software or on a screen presented to the user during the installation process. The functions may be designed to analyze which Internet sites the user visits and to present advertising pertinent to the types of goods or services featured there. The term is sometimes used to refer to software that displays unwanted advertisements.

- Logic Bomb: Logic bombs like adware or rootkits could be spread by worms if they exploit the right service and gain root or admin access on a computer.

The following reference(s) was used to create this question:

The CCCure CompTIA Holistic Security+ Tutorial and CBT

and

http://en.wikipedia.org/wiki/Rootkit

and

http://en.wikipedia.org/wiki/Computer_worm

and

http://en.wikipedia.org/wiki/Adware