In plain English
Malware is any software that does something you didn't agree to and wouldn't want. This covers everything from ransomware that encrypts your files, to trojans that silently give attackers remote access, to spyware that records your keystrokes and sends them to a criminal server.
Full definition
Malware is software that does something the device owner did not agree to and would not want if they understood what was happening. The category is broad because intent varies: some malware is built to make money, some to cause damage, some to maintain persistent access for later use.
The forms that affect Australian businesses most frequently are , which encrypts files and demands payment for the decryption key; trojans, which masquerade as legitimate software while giving an attacker remote access to the device; and information stealers, which record credentials, session cookies, or keystrokes and send them back to a criminal infrastructure. A single infected machine holding cached credentials can become the entry point for a much larger compromise.
Delivery is usually through email attachments, malicious links, or software downloaded from untrusted sources. The addresses malware through application control, which prevents unapproved software from running, and through patching operating systems and applications to close the vulnerabilities malware exploits. Microsoft Defender, included in Business Premium, provides real-time malware detection and integrates with for device management. The 's Annual Cyber Threat Report 2022-23 identified ransomware as one of the most destructive threats to Australian organisations, noting that small businesses are targeted because they often lack the detection capability to catch an infection before it spreads.