EMZETT.AIDS Trojan
In short: The AIDS trojan of 1989 is considered the first known ransomware.
In more detail: The biologist Joseph Popp sent thousands of floppy disks supposedly containing an AIDS information program to participants of a WHO conference. After 90 starts of the computer the program encrypted file names and demanded 189 US dollars by post to a P.O. box in Panama.
In Depth
Technology
The encryption was simple (symmetric), the key was inside the program. A remedy was therefore easy to develop.
Significance
The case shows the basic pattern of today’s ransomware: deception, encryption, ransom demand. The distribution channel back then was the floppy disk, today it is phishing and security holes.