Millenium RAT Versions Explained
From the .NET 2.4 / 2.5 branch to the native C++ 4.x rewrite — what changed and what it means for defenders.
What versions of Millenium RAT exist? Public research documents Millenium RAT 2.4 (analyzed by CYFIRMA, November 2023, .NET), version 2.5 (reported shortly after), and the 4.x branch (analyzed by Group-IB, June 2026, native C++ with libcurl and Telegram Bot API C2). Individual sub-version labels such as 4.1 or 4.2 should be differentiated by source: vendor research, sandbox sample labels, or confirmed developer releases.
| Attribute | 2.4 | 2.5 | 4.x |
|---|---|---|---|
| Publicly analyzed | November 2023 | November 2023 | 2026 (Group-IB, June 25) |
| Architecture | .NET (managed) | .NET (managed) | Native C++ |
| Platform | Windows | Windows | Windows |
| C2 | Telegram Bot API | Telegram Bot API | Telegram Bot API (libcurl) |
| Research source | CYFIRMA | CYFIRMA | Group-IB |
| MaaS model | Lifetime ~US$30 | Continued development | US$50 / US$10 / US$90 |
| Global telemetry | — | — | 62,289 endpoints / 160+ countries |
- Analyzed
- November 2023
- C2
- Telegram Bot API
- Source
- CYFIRMA
First publicly analyzed version. Win32 / .NET executable. Strong structural similarity to ToxicEye Telegram RAT.
- Analyzed
- November 2023
- C2
- Telegram Bot API
- Source
- CYFIRMA
Reported shortly after 2.4. Continued development. Less extensively documented publicly.
- Analyzed
- 2026 (Group-IB, June 25)
- C2
- Telegram Bot API (libcurl)
- Source
- Group-IB
Substantial architectural rewrite. Removes .NET dependency. MaaS subscription model. 62,289 endpoints / 160+ countries in telemetry.
A note on sub-version labels
If individual versions such as 4.1 or 4.2 are mentioned in research, differentiate between vendor research, sandbox sample labels, and confirmed developer releases. This resource does not invent version chronology and only documents versions established by primary research sources.
- ▸2.4: first publicly analyzed (CYFIRMA, Nov 2023), .NET, Telegram C2.
- ▸2.5: reported shortly after 2.4; less extensively documented publicly.
- ▸4.x: native C++ rewrite (Group-IB, June 2026), libcurl, MaaS, global telemetry.
- ▸Sub-version labels must be sourced — never invent version chronology.
