Malware is software designed to harm, disrupt, or gain unauthorized access. The category covers viruses, worms, trojans, ransomware, spyware, and rootkits. Each behaves differently. A virus attaches to a file and spreads when the file runs. A worm spreads on its own across networks. A trojan disguises itself as legitimate software. Ransomware encrypts files and demands payment. Spyware steals data quietly. A rootkit hides deep in the operating system, making itself and other malware hard to find.

Delivery methods vary. Phishing emails with malicious attachments. Drive-by downloads from compromised websites. Infected USB drives. Supply chain attacks that plant malware in legitimate software updates. The SolarWinds breach in 2020 used that last method to compromise thousands of organizations, including US government agencies. Malware is not going away. It is a business. Ransomware-as-a-service lets criminals rent the tools without building them. Affiliates pay a cut to the developers. The ecosystem is professionalized. Defense requires layered controls: email filtering, endpoint protection, network monitoring, and user training. No single tool catches everything. Malware authors test their creations against common defenses before releasing them. The arms race continues.

Malware types

• Virus — attaches to files, spreads when executed
• Worm — self-replicating, spreads across networks
• Trojan — disguises itself as legitimate software
• Ransomware — encrypts data for payment
• Spyware — steals information quietly

Malware is the weapon. The attacker is the hand holding it. Block the delivery, and the weapon never reaches the target.