Malware is a term that is used to describe a wide range of malicious software code designed expressly for the purposes of infiltrating a computer without the user’s knowledge or consent. Malware tools are typically used by malicious hackers looking to steal data from a user’s computer, to sabotage it or to take complete control of the system for various nefarious purposes.

Until fairly recently, the most prevalent forms of malware programs were computer viruses and worms. A virus is software code that is designed to infect a user’s computer and run some kind of malicious command, such as erasing data, every time a specific application is opened or executed. Worms on the other hand are designed to infect a computer and then to automatically propagate to other computers via the Internet.
Over the past few years, the term malware however has been used to describe a much wider category of malicious software. Today, examples of malware programs include not just viruses and worms but also rootkits, Trojan horse programs, keystroke loggers, password sniffers, spyware, adware and backdoor programs.

Many of these malicious programs were developed in response to the increasingly sophisticated methods employed by anti-virus software to detect, block and delete older worms and viruses from infected machines. Trojan horse programs for example are designed specifically to evade detection by anti-malware software. Such programs can appear harmless and are often concealed in desirable pieces of software code such as a free music or free video download. Users who are tricked into installing such programs can find their systems becoming quickly infected with a worm, virus or other piece of malware.

Rootkits meanwhile are another type of malware program designed to stealthily infect a user’s computer and to remain hidden from anti-virus software. They allow malicious hackers to take complete administrative control of a compromised computer from a remote location for the purposes of relaying spam, pornography and other malicious software. Backdoor programs allow criminals to break into a computer without having to enter any username, password or other log-in credentials.

Adware and spyware programs represent a different sort of malware threat. Though such programs are not always designed to be malicious they can be extremely annoying from a user’s standpoint. Adware programs, which are often hidden in Trojan horses, for instance are used to constantly serve up pop-up advertisements to users. Spyware programs on the other hand enable the stealthily tracking, monitoring and collection of a user’s Web browsing habits for the purposes of serving up targeted advertisements.