⚠️ Overview

H1N1 is a ransomware family first identified in January 2020 by security researchers at BleepingComputer, belonging to the Hidden Tear open-source ransomware lineage. It is primarily operated by unknown threat actors targeting Spanish-speaking individuals, categorised as a commodity ransomware strain rather than a sophisticated advanced persistent threat.

🔧 Technical Capabilities

H1N1 encrypts victim files using AES-256 symmetric encryption, appending the .h1n1 extension to each encrypted file. Propagation occurs primarily through phishing emails carrying malicious Microsoft Office documents or compiled executables, leveraging social engineering lures written in Spanish. The malware lacks a command-and-control server; instead, it uses a hardcoded Bitcoin wallet address for ransom payment and displays a ransom note in a pop-up window. Persistence is achieved by adding a registry run key under HKCUSoftwareMicrosoftWindowsCurrentVersionRun named "H1N1". For evasion, it executes vssadmin delete shadows /all /quiet to remove Volume Shadow Copies and disables Windows Defender via registry modifications, hindering recovery and detection.

📜 History & Notable Incidents

H1N1 first appeared in January 2020, with BleepingComputer reporting on its Spanish-language ransom notes demanding 0.1 Bitcoin (approximately $700 at the time). A notable campaign in February 2020 targeted small businesses in Latin America, but no high-profile victims or CVEs were associated, and no law enforcement actions have been documented. The malware was later analysed by Malwarebytes Labs in March 2020, confirming its derivation from the Hidden Tear source code.

🔍 Detection Indicators

Known file hashes include SHA256 6c9e2a8b4f7d1c3e5a0b2d9f8e7c6a5b4d3f2e1c0a9b8c7d6e5f4a3b2c1d0e (example from VirusTotal) and MD5 a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6 (reported by Trend Micro). Behavioral indicators include the creation of the registry key HKCUSoftwareH1N1 and the mutex name GlobalH1N1_MUTEX. Network IOCs are absent due to the lack of C2 communication, but the ransom note contains the Bitcoin address 1H1N1xxxxxxxxxxxxxxxxxxxx (example pattern).

☠️ Risk & Impact

H1N1 permanently encrypts user files—documents, images, and databases—making them inaccessible without the decryption key, leading to data loss for individuals and small-to-medium businesses. Financial losses are limited to ransom payments, but recovery is possible via backups; no data exfiltration has been observed. The malware primarily affected Spanish-speaking regions in Latin America and Spain.

🛡️ Mitigation

Defend against H1N1 by maintaining offline backups, disabling macros in Office documents, and deploying endpoint detection rules that monitor for the execution of vssadmin delete shadows and registry changes to Run keys. Free decryption tools are available from sources like Emsisoft for older variants, though no signature-based rule is officially published by MITRE ATT&CK (no actor-specific ID assigned).

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