Scareware
A term used to describe software that scares the users into purchasing the full program. A good example of scareware is a program claiming it's an anti-virus or other security protection program and that it's found dozens of potential threats on the computer, which in reality are either nonexistent or not really a threat to the user or his or her computer.
Most scareware is installed onto a computer though false Internet advertisements, other free programs, and other malware. Although some of these programs can be uninstalled through Add/Remove programs in Windows, some may require a special anti-malware tool such as Malwarebytes in order to be removed.
Also see: Malware, Ransomware, Security definitions