Hidden Tear targets Windows OS and is the first open-source, modifiable ransomware kit. It uses AES encryption and claims to be undetectable by antivirus software. Its developers advertise its release as being “only for educational purposes” but one hacking group has already been discovered using a modified version of the ransomware to infect victims. Files encrypted by Hidden Tear will gain a .locked file name extension.
UPDATE 11/7/2016: A new Hidden Tear variant was discovered impersonating Cerber. It appends .cerber to the names of encrypted files and produces a ransom note named HOW_TO_RESTORE_YOUR_DATA.html.
UPDATE 1/5/2017: A new version called Depsex or MafiaWare appends .Locked-by-Mafia to encrypted files and drops a ransom note named READ_ME.txt.
UPDATE 2/26/2017: A new variant appends .BarRax to file names.
UPDATE 3/22/2017: A new version appends .AngleWare to encrypted file names.