“Malware”, short for malicious software, is an umbrella term that refers to any software program deliberately created to perform an unauthorized and often harmful action. It is a simple combination of two words created to allow people to talk about viruses and all other forms of malicious software in a general manner.

Viruses, backdoors, keyloggers, password stealers, and other Trojan horse programs, Word and Excel macro viruses, boot sector viruses, script viruses (batch, windows shell, java, etc.) and Trojans, crimeware, spyware and adware are but a few examples of what is considered malware.

It was inevitable that the term malware would come about. It was once sufficient to call something a 'virus' or 'Trojan horse', because at one time that's about all that existed in a landscape consisting mostly of DOS-based PCs. There were “worms”, but worms affected only UNIX boxes and were of no great concern. Infection methods and vectors evolved, however. The terms virus and Trojan no longer provide a satisfactory definition for all the types of rogue programs that exist. Several examples follow:

• viruses attach themselves to application files and often reduce the PC's performance
• a Trojan may function as a password-stealer, making it possible for somebody to see confidential login ID and user-password information.
• A vulnerability may lead to an exploit that allows an attacker complete control over the PC.
• Ransomware, actually a form of a Trojan, encrypts files. Its unique characteristic is that the attacker then demands money from the user of the affected PC in order to receive the decryption key.
• Crimeware, an umbrella term in itself, refers to a malicious program deliberately programmed to initiate some form of crime. These programs are typically Internet-based, and are usually closely associated to some form of identity theft.