Scareware refers to
|“||malicious pop-ups that exploit concerns about Internet safety by issuing false warnings just to sell software to "fix" the imagined problem.||”|
It is a computer program meant to deceive a user into believing that something is wrong with their computer or that malware has been installed. Generally, the scareware itself is the malware, either already downloaded onto the computer, or that will be downloaded if the user agrees to install/use the program.
A popular example of scareware is a pop-up ad that appears when you visit a certain website that informs you that you may already have a virus on the computer. The ad then prompts the user to click to download a free antivirus software that inevitably loads a virus onto the computer.