RensenWare

RensenWare is a ransomware trojan for Microsoft Windows released in April 2017. It was created by Park Shinjo as a prank on his friends, but it managed to spread throughout the world in a few days. When RensenWare finishes encrypting a computer's files, it will display a ransom note and official artwork of Captain Minamitsu Murasa from Touhou 12: Unidentified Fantastic Object.

Why it Sucks

 * 1) It encrypts almost every file on the user's computer in a .RENSENWARE format and won't decrypt them unless you score 200 million points in Touhou 12: Unidentified Fantastic Object on the hardest difficulty. The game isn't bundled with the software, however, so you can say goodbye to your files if you don't own it. You're also doomed if you're not great at playing Touhou 12.
 * 2) If you attempt to force quit the Rensenware process, you will lose your encrypted files forever.

Redeeming Qualities

 * 1) If the ransomware attempts to encrypt a file it cannot encrypt, it will crash as it will attempt to encrypt files on all drives.
 * 2) There are software available that can decrypt infected files.