Port 1781: answersoft-lm — A Registered Port with a Ghost Behind It

Port 1781 sits in the registered port range and carries an official IANA assignment: answersoft-lm, a license manager for software by a company called AnswerSoft. The registration covers both TCP and UDP.¹

Beyond the name, the trail goes cold. AnswerSoft and its license manager have left almost no documentation on the modern Internet. The company does not appear to have a current web presence, and no meaningful technical documentation for the protocol survives in readily findable form. Port 1781 is, in practice, a ghost — named but abandoned.

What the Registered Range Means

Ports 1024 through 49151 are registered ports. Unlike the well-known ports below 1024 (which require root or administrator privileges to bind on most systems), registered ports can be used by any process with ordinary permissions.

The registration system works on the honor system. IANA records who asked for a port and what they said they'd use it for. There is no enforcement, no expiration, and no mechanism to reclaim a registration when a company closes or a product is discontinued. Port 1781 is one of many such orphaned assignments scattered through the registered range.²

No Known Malware Associations

Port 1781 has no documented associations with malware or trojans. Its obscurity appears to be benign — a product that was niche and is now defunct, not a port with a dark history.

How to Check What's Listening on This Port

If you see traffic on port 1781 and want to know what's using it:

On Linux/macOS:

# Show the process listening on port 1781
ss -tlnp | grep 1781

# Or with lsof
lsof -i :1781

On Windows:

# Show the process ID bound to port 1781
netstat -ano | findstr :1781

# Then identify the process
tasklist | findstr <PID>

In nearly all cases, you will find nothing — port 1781 simply goes unused on most systems.

Why Ghost Ports Matter

The registered port range has over 48,000 slots. A significant portion point to software that no longer exists, companies that have closed, or protocols that were never widely deployed. This is not a failure — it reflects the reality that software ecosystems change faster than registries can adapt.

Ghost ports like 1781 serve an indirect purpose: they hold a name, preventing confusion if someone else tries to use the same number for something new. A port with a name, even a forgotten one, is less likely to become a source of ambiguity than a truly unrecorded number.