Answer: Computer viruses
Step-by-step explanation:
Computer viruses are programs that need to be attached to other files to install themselves on computers without the users’ knowledge or permission and spread—sometimes very rapidly. A spyware is also a program that installs itself on a computer without the user's knowledge and tries to collect sensitive information such as passwords, credit card details and sends this information to a remote computer. A computer worm is a type of a virus that replicates itself across different computers. Freeware on the other hand is software that can be obtained for free.