Hidden Tear

Hidden Tear is an open-source ransomware family released in 2015 as an educational proof of concept and subsequently widely abused by threat actors as the basis for numerous real-world ransomware variants. It is a .NET/C# file-encrypting malware strain that uses AES to encrypt victim files, writes a ransom note, and transmits encryption material and basic host information to a remote server. The codebase includes configurable target file extensions and can be readily modified, which has made it a common foundation for derivative ransomware used in opportunistic and targeted intrusions.

Hidden Tear is notable less for technical sophistication than for its influence on the ransomware ecosystem. Multiple later families and one-off campaigns have been assessed as heavily based on or directly derived from its source code, including variants used in COVID-19-themed phishing operations, campaigns targeting Brazilian users, and bespoke ransomware deployed during broader post-compromise activity. Analysts have repeatedly identified code reuse through shared function structure, encryption logic, and residual project artifacts. Because the source was publicly available, minor edits to strings, ransom notes, target paths, extensions, and network configuration were often sufficient for actors to generate new variants and evade simple signature- or hash-based detections.

Operationally, Hidden Tear and its descendants have been associated with a wide range of actors, from novice criminals to more established intrusion operators. It has appeared in commodity ransomware campaigns, enterprise-targeting incidents, and hands-on-keyboard intrusions where publicly available ransomware was used as a final-stage encryption tool. The family has also been referenced in reporting on actors possessing or deploying public ransomware tooling alongside custom malware and legitimate encryption utilities.

Hidden Tear primarily targets Windows systems. Its historical significance lies in lowering the barrier to entry for ransomware development by providing functional, modifiable source code that accelerated the proliferation of copycat ransomware and derivative extortion malware.