A malware virus is a catch-all term for any annoying or harmful software that makes its way onto a computer or a network without the owner's awareness. The word "malware" comes from the phrase "malicious software." Software is considered to be malware depending on what the intention of its creator was. Computer viruses, worms, Trojan horses, spyware or any other form of unwanted software can be considered a malware virus. It is important to distinguish a malware virus from "bugs" or small defects in otherwise legitimate software.
A variety of purposes can be served by a malware virus, from simple pranks or vandalism, to making a financial profit for its creator. Throughout the early history of malware in the 1980s and 1990s, almost every malware virus was written for the sole purpose of playing a prank. Among the less-harmful viruses that circulated during this time was one that opened up all the text documents in a hard drive, and changed every instance of the word "and" to "not." A virus is technically defined as malware that requires intervention on the part of the computer user in order to function, such as opening up a malicious email attachment. Worms are variants of viruses, and may accomplish the same purpose, but are more insidious since they work on their own, without user intervention.
One of the more infamous and dangerous types of malware viruses that have been seen is the Trojan horse virus. This is a group of viruses that make their way onto a computer, and act as something of a ticking time bomb. At the appointed time, they can erase a hard drive or steal confidential information before rendering the person's computer essentially inoperable. Trojan horse viruses typically present themselves as something that they are not, in order to gain access to a computer hard drive and conceal themselves.
More recently, it has been common to see malware viruses that attempt to make a profit from stealing personal information from a computer user. Keystroke loggers are one example of this newer kind of malware. Their purpose is to keep track of every keystroke that is made on a computer, in order to mine data such as passwords, credit card numbers and other sensitive information. This financially motivated malware is often referred to as crimeware or spyware, and can be some of the most troublesome malware in existence.
Fortunately, there are many ways in which computer users can protect themselves from the threat of a malware virus. Anti-virus and anti-spam software are good places to start, and are recommended for those who own a computer that runs a Windows™ operating system. It is usually not considered necessary on computers with other operating systems, since most viruses are not written in a way that targets them.