architecture

A significant evolution of the Millenium remote access trojan (RAT) has impacted over 62,000 Windows devices across more than 160 countries. The latest version, 4.*, marks a departure from previous .NET-based versions and is attributed to a threat cluster known as Y2K Operators, with the creator identified as “ShinyEnigma.” There are 62,289 infected endpoints, with 39,730 infections occurring in the first quarter of 2026. The RAT is marketed as malware-as-a-service (MaaS) and promoted through underground forums and platforms like GitHub, with accessible pricing. Millenium RAT 4 is developed in native C++ and uses the Telegram Bot API for command-and-control communications. Its capabilities include stealing browser data, collecting system information, logging keystrokes, capturing screenshots and audio, accessing Telegram and Discord data, downloading additional payloads, and executing Windows or PowerShell commands. The malware ensures persistence by replicating itself in the %APPDATA% directory and creating an autorun registry entry. The malware is distributed through social engineering tactics such as cracked software, cryptocurrency utilities, hacking toolkits, OSINT tools, exploit builders, and Roblox-related cheats. Some campaigns have trojanized malware builders, infecting cybercriminals. One campaign used PDF-themed lures with a malicious Windows shortcut to download the RAT while displaying a legitimate document. Payloads often use filenames associated with Windows components or security software to blend into infected systems. Group-IB recommends avoiding untrusted executables, applying security updates, enabling multi-factor authentication, and monitoring for unusual autorun registry entries.