Malware

Network security means protecting devices and data from illegitimate access or misuse. The biggest threat is malware: malicious software, written to harm a computer or steal from its user. Know each kind by how it spreads and what it wants:

• Virus: code that attaches itself to a program or file, and runs when that program is opened. Like a biological virus, it needs a host, and spreads when infected files are shared.
• Worm: a standalone program that spreads by itself across a network, without needing a host file or any action by the user.
• Ransomware: locks the computer or encrypts the user's files, then demands a payment (ransom) to release them. The WannaCry attack of 2017 hit computers in many countries.
• Trojan: looks like a legitimate, useful program, but secretly does harm, as in the story of the wooden Trojan horse.
• Spyware: secretly collects information about the user (habits, passwords) and sends it to someone else.
• Adware: shows unwanted advertisements, to earn money for its makers.
• Keylogger: records every key the user presses, to steal passwords and card numbers.

One defence against keyloggers is an online virtual keyboard, whose keys appear in a random layout each time, clicked with the mouse: the recorded key presses then reveal nothing.