Port 3151: Unassigned — A Quiet Port in a Noisy Neighborhood

Port 3151 has no officially assigned service. IANA lists it as unassigned for both TCP and UDP.

The Registered Port Range

Port 3151 lives in the registered ports range (1024–49151). This range is different from the well-known ports below 1024 — no root privileges are required to open a port here, and assignment is more loosely enforced.

IANA maintains a registry for this range, but registration is voluntary. Thousands of ports sit unassigned, available for any application to claim. Some get picked up by commercial software that never bothered with formal registration. Others get used once and abandoned. Most stay empty.

The nm-assessor Ghost

Some older port databases list port 3151 under the name nm-assessor (NetMike Assessor), a network assessment tool. The entry appears with "RFC Doc 0" — meaning there is no specification behind it, no standards document, no formal protocol definition. The name exists in port registries without the software to back it up. Whatever NetMike Assessor was, it left few traces.

The Mydoom Shadow

Port 3151 sits inside the range 3127–3198, which is where Mydoom's backdoor operated.

Mydoom (also called Novarg) arrived in January 2004 and became the fastest-spreading email worm in history at that time. When it infected a machine, it opened a backdoor that listened on the first available TCP port between 3127 and 3198, turning the host into a proxy that attackers could use for further campaigns.¹ The Deadhat worm (W32.HLLW.Deadhat) subsequently exploited Mydoom-infected machines, entering through these same open ports.²

Mydoom is long dead. But the memory lingers in intrusion detection signatures and security tooling — traffic on ports in this range still gets a second look.

What to Do If You See Port 3151 Open

If port 3151 shows up open on a machine you're investigating, check what's listening:

Linux / macOS:

# Show the process listening on port 3151
sudo ss -tlnp | grep 3151
# or
sudo lsof -i :3151

Windows:

netstat -ano | findstr :3151

Match the PID from those commands against your process list (ps aux on Linux, Task Manager on Windows). If you don't recognize the process, investigate before assuming it's benign.