What is malware? Viruses, worms, trojans, and beyond

Malware—a blanket term for viruses, worms, trojans, and other harmful computer programs—has been with us since the early days of computing. But malware is constantly evolving and hackers use it to wreak destruction and gain access to sensitive information; fighting malware takes up much of the day-to-day work of infosec professionals.

Malware definition

Malware is short for malicious software, and, as Microsoft puts it, “is a catch-all term to refer to any software designed to cause damage to a single computer, server, or computer network.” In other words, software is identified as malware based on its intended use, rather than a particular technique or technology used to build it.

Types of malware

This means that the question of, say, what the difference is between malware and a virus misses the point a bit: a virus is a type of malware, so all viruses are malware (but not every piece of malware is a virus).

There are a number of different ways of categorizing malware; the first is by how the malicious software spreads. You’ve probably heard the words virus, trojan, and worm used interchangeably, but as Symantec explains, they describe three subtly different ways malware can infect target computers: