Malware (malicious software) refers to a variety of harmful programs that can ‘infect’ a computer.
Note
The listed malware below are defined by how they spread, not what the do to a system once they’re on it. Any of these can be used to compromise any point of the CIA Triad. There are also very many more types of malware than what is listed here.
Viruses
Viruses infect other software (a ‘host program’). The virus spreads as the software is shared by users. Viruses are capable of corrupting or modifying files on target computers, among other nefarious activities.
As viruses spread by being shared alongside other software, free software, such as demos, shareware, and pirated software, are common vectors for infection.
Worms
Worms, unlike viruses, don’t require a host program. They are standalone and are able to spread on their own, without user interaction. Worms can congest a network, which is bad, but they often carry a ‘payload’ which can cause harm to target devices.
Trojan Horses
Trojan Horses are harmful software that is disguised as legitimate software. They are spread through user interaction such as opening email attachments, or downloading a file from the Internet.