A type of ransomware that blocks a computer or mobile device, usually with a ransom demand. Unlike cryptors, blockers do not encode user data, but render the system unusable. Such malware typically displays a non-closeable message with a payment demand on top of all other windows.
Sometimes blockers target individual applications, for example, a browser, instead of the device as a whole. A particular and not illegal instance of a blocker is one that displays a window prompting the user to buy the full version of a program at the end of a trial period.