A worm is a type of software that, while not definitely malicious, has a suspicious or potentially unwanted aspect to it.

Ransomware is a malicious self-replicating computer program that penetrates operating systems to spread malicious code to other computers.

Spyware is software that collects and reports information about a computer user without the user’s knowledge or consent.

A Trojan horse is a software program that, while not definitely malicious, monitors and logs the keys pressed on a system’s keyboard.