Malware

Malware is the umbrella term. A trojan disguises itself as legitimate software. A worm spreads by itself across networks. Spyware and infostealers collect information quietly. Loaders install other malware. Ransomware encrypts files for extortion.

Delivery methods change over time. Malicious macros in Office documents were common until Microsoft began blocking macros from internet files by default. Attackers shifted to ISO files, OneNote attachments, HTML smuggling, fake browser updates, poisoned search ads and malicious installers for popular free tools.

Traditional antivirus catches known malware by signature, which still helps. But much modern intrusion activity uses legitimate tools already on the system, an approach called living off the land, which no signature will flag. That is why businesses have moved to EDR, which watches behaviour, and to application allowlisting on high-value systems.

For a small business, the basics remain effective: keep systems patched, restrict local admin rights, filter email and web traffic, and make sure someone reviews EDR alerts promptly.