⚠️ Overview

HildaCrypt is a file-encrypting ransomware first discovered in June 2016 by MalwareHunterTeam. It belongs to the Hidden Tear family of open-source ransomware, written in C# .NET. The malware is attributed to an individual or group using the alias "Hilda" and is categorized as a ransomware that encrypts user files and demands a ransom payment in Bitcoin for decryption.

🔧 Technical Capabilities

HildaCrypt uses AES-256 encryption to lock files and appends the .hildacrypt extension. The encryption key is generated locally and stored in the Windows registry under HKCUSoftwareHildaCrypt as a binary value. After encryption, the ransomware deletes its own executable to hinder analysis. Persistence is achieved via a registry run key at HKCUSoftwareMicrosoftWindowsCurrentVersionRun named "HildaCrypt". For evasion, it checks for sandbox environments by enumerating window titles such as "sandbox" or "dbg" and terminates if detected. Propagation relies on social engineering via spam email attachments; it does not spread laterally. The ransom note READ_IT.txt contains ASCII art of a cat and demands 0.5 Bitcoin to a hardcoded wallet address, with instructions to contact the attacker via email.

📜 History & Notable Incidents

First observed in June 2016, HildaCrypt was distributed through phishing campaigns with malicious .NET executables. No large-scale attacks against high-profile organizations have been publicly documented; infections targeted individual users. No CVEs are associated. In July 2016, security researcher Michael Gillespie added HildaCrypt decryption support to the ID-Ransomware platform, allowing victims to recover files if the offline encryption key remains. Law enforcement have not conducted takedowns.

🔍 Detection Indicators

Behavioral indicators include files with .hildacrypt extension, a ransom note READ_IT.txt, and a mutex named "HildaCryptMutex". Registry modifications include a key at HKCUSoftwareHildaCrypt and a run key named "HildaCrypt". Network indicators are minimal; the ransomware may attempt to check internet connectivity by contacting google.com. File hashes for HildaCrypt samples have been published by MalwareHunterTeam and BleepingComputer. The executable is typically ~200 KB and is a .NET assembly. User-Agent strings are not used.

☠️ Risk & Impact

HildaCrypt encrypts common file types including documents, images, videos, and databases, rendering them inaccessible without the key. The ransom is set at 0.5 Bitcoin (approximately $300 at the time of infection). Many victims chose not to pay due to available free decryption tools. The ransomware primarily affected individual home users and small businesses; no major corporate breaches are known. Data exfiltration is not performed.

🛡️ Mitigation

Recommended defenses include maintaining regular offline backups, enabling Volume Shadow Copy, and avoiding suspicious email attachments. Decryption tools from ID-Ransomware (Michael Gillespie) and antivirus vendors can recover files if the encryption key is still on the system. All major antivirus products detect HildaCrypt with updated signatures.

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