The word "malware" comes from the term MALicious softWARE. Malware is any software that infects and damages a computer system without the owner's knowledge or permission. Malware includes computer viruses, computer worms, Trojan horses, spyware, crimeware, rootkits, backdoors and keystroke loggers.
A computer virus is malware that spreads from one computer system to the next without the user's knowledge or permission by attaching itself to legitimate files and programs.
A computer worm is similar to a virus, except that it does not need to attach itself to spread. It uses security vulnerabilities within a network.
A Trojan horse is a program that appears harmless but is not. An example of a Trojan horse is a file that says it is a software update, when it is actually a program designed to harm your computer.
Spyware is any program that tracks information about you and sends it to someone else, usually in an effort to display advertisements on your computer.
Crimeware is a term that was created to identify malware that was designed with the intention of perpetrating a crime, usually identity theft.
Rootkits, Backdoors and Keystroke Loggers
Rootkits, backdoors and keystroke loggers are methods or programs that malware uses to access information or prevent detection. A rootkit is a system that malware can use to prevent detection by modifying the operating system software. Backdoors is a method that allows malware to bypass the normal procedures of a system to gain access. Keystroke loggers are programs that logs what is typed on a computer and sends it to a third party.