Malware: What is it?
Malware: Malware is basically all the bad software out there (word comes from Malicious and Software) that is designed to break into your computer and either damage it, steal information, or in some cases, just annoy you! (some of the hackers who write this stuff are just painful people with too much time on their hands!) Malware includes viruses, worms, torajan horses, rootkits, spyware, adware, and crimeware. These terms are often used interchangeably, but they are actually all different kinds of malicious software.
Virus: “A computer virus is a computer program that can copy itself and infect a computer without the permission or knowledge of the owner... A true virus can only spread from one computer to another (in some form of executable code) when its host is taken to the target computer; for instance because a user sent it over a network or the Internet, or carried it on a removable medium such as a floppy disk, CD, DVD, or USB drive.” - Wikipedia
Worm: “A computer worm is a self-replicating computer program. It uses a network to send copies of itself to other nodes (computers on the network) and it may do so without any user intervention. Unlike a virus, it does not need to attach itself to an existing program. Worms almost always cause at least some harm to the network, if only by consuming bandwidth, whereas viruses almost always corrupt or devour files on a targeted computer.” - Wikipedia
Trojan Horse: “The Trojan horse, also known as trojan, in the context of computing and software, describes a class of computer threats (malware) that appears to perform a desirable function but in fact performs undisclosed malicious functions that allow unauthorized access to the host machine, giving them the ability to save their files on the user's computer or even watch the user's screen and control the computer. Trojan Horses can be easily and unwittingly downloaded. For example, if a computer game is designed such that, when executed by the user, it opens a back door that allows a hacker to control the computer of the user, then the computer game is said to be a Trojan horse. However, if the computer game is legitimate, but was infected by a virus, then it is not a Trojan horse, regardless of what the virus may do when the game is executed. The term is derived from the classical story of the Trojan Horse.” - Wikipedia
Rootkit: “A rootkit is a software system that consists of a program or combination of several programs designed to hide or obscure the fact that a system has been compromised.” - Wikipedia
Spyware: “Spyware is computer software that is installed surreptitiously on a personal computer to collect information about a user, their computer or browsing habits without the user's informed consent.” - Wikipedia
Adware: “Adware or advertising-supported software is any software package which automatically plays, displays, or downloads advertisements to a computer after the software is installed on it or while the application is being used. Some types of adware are also spyware and can be classified as privacy-invasive software.” - Wikipedia
Note: Not all adware is harmful. Some software programs use advertising within them in order to make them free. Ideally, this means that the developers have an incentive to continue to develop great software, users get free software and advertisers get exposure. There is often an option with this software to buy a 'registered' version, which won't have any ads. Some people find the advertising annoying, in which case they can just uninstall the software. However some adware can download other unwanted software, and some of it is spyware. The best advice is to just be careful when downloading any software, and do a little bit of background research before you install any unknown software.
- Crimeware: “Crimeware is designed to perpetrate identity theft in order to access a computer user's online accounts at financial services companies and online retailers for the purpose of taking funds from those accounts or completing unauthorized transactions that enrich the thief controlling the crimeware. Crimeware also often has the intent to export confidential or sensitive information from a network for financial exploitation. Crimeware represents a growing problem in network security as many malicious code threats seek to pilfer confidential information.” - Wikipedia
Fortunately, it is relatively simple to protect yourself from these security threats. See the 'How do I protect myself on the web?' section.