Not every piece of software that attacks your PC is a virus. Computer viruses are just one kind of malware (mal-icious soft-ware). Here are some of the other, most common kinds:
•Trojans: like the ancient wooden horse full of attackers it takes its name from, this malware pretends to be harmless legitimate software, or comes embedded in it, in order to trick the user and open up the gates for other malware to infect a PC.
•Spyware: with examples such as keyloggers, this kind of malware is designed to spy on users, save their passwords, credit card details, other personal data and online behavior patterns, and send them off to whoever programmed it.
•Worms: this malware type targets entire networks of devices, hopping from PC to PC.
•Ransomware: this malware variety hijacks files (and sometimes an entire hard drive), encrypts them, and demands money from its victim in exchange for a decryption key (which may or may not work, but it probably won’t).
•Adware: this exceedingly irritating kind of malware floods victims with unwanted ads, and opens up vulnerable security spots for other malware to wiggle its way in.