Ransomware

Ransomware is a category of Malware that is seen when a Trojan Horse takes over a computer and encrypts the victim's hard drive, charging money to decrypt it, hence the "ransom".

First known case

In 1989 the AIDS Trojan was written, claiming to offer information about AIDS and HIV. When victims ran the program, the trojan would encrypt their HDD and display a message demanding money in exchange for a password that could be used to decrypt the hard disk and recover their files. If the user did not pay, the drive would remain encrypted indefinitely & the victim would not be able to access any of their files and/or programs.