Viruses or malware can come in a variety of forms:
Malware is an abbreviation for malicious software. Malware is designed to infiltrate a computer system without the owner's informed consent. The expression is used by computer pros to mean a variety of forms of hostile, intrusive, or annoying software or program code.
A Trojan horse is a computer program that claims to do one thing, such as play a game, but has hidden parts that can erase files or even your entire hard drive. The term is derived from the Trojan Horse story in Greek mythology.
Spyware is a computer program that downloads with another program from the Internet. Spyware can monitor what you do, keep track of your keystrokes, discern credit card and other personal identification numbers, and pass that information back to the person who wrote the program.
Spyware is known to change computer settings, resulting in slow connection speeds, different home pages, and/or loss of Internet or functionality of other programs.
A malicious website or program that tries to trick or scare users into downloading and/or purchasing unnecessary, potentially dangerous software.
Malware that threatens to publish the victim's data or perpetually block access to it unless a ransom is paid.