What Port 3330 Is
Port 3330 sits in the registered port range (1024-49151). These ports are assigned by IANA to specific services, but unlike well-known ports below 1024, any process can open them without administrator privileges. IANA tracks them, but the tracking is only as meaningful as the software behind the registration.
In port 3330's case, the software barely exists.
The Registered Service: MCS Calypso ICF
IANA assigned port 3330 to mcs-calypsoicf, the "MCS Calypso ICF" service, belonging to Micro Computer Systems. Calypso was an email client released in 1996, positioned as a successor to the popular Pine email client. It had a following among technical users who liked its keyboard-driven interface.
The "ICF" almost certainly stood for some internal communication framework the client used. But Calypso faded. Micro Computer Systems stopped active development. The port registration outlived the software by decades, which is common: IANA rarely revokes assignments, so ports can sit registered to dead products indefinitely.1
If you see port 3330 open on a machine today, it is almost certainly not Calypso.
The More Memorable History: Randex
In 2003, port 3330 became part of something less obscure. Worm:Win32/Randex was a network worm that spread by targeting Windows machines with weak or default passwords. Once installed, Randex opened ports 3330, 3331, and 3332 to receive remote commands, effectively turning infected machines into a botnet that its author could control.2
Randex also dropped TrojanProxy:Win32/Roxy.A on infected systems, a secondary payload that turned compromised machines into proxy servers, routing traffic through them to obscure the worm author's identity and activities.3
The author was a 16-year-old from Mississauga, Ontario. He was arrested in May 2004 after an investigation traced the worm back to him. He had collaborators in the United States and Britain.4
Port 3330 did not make him harder to catch.
Security Considerations
If you find port 3330 open on a machine:
- It is almost certainly not MCS Calypso
- It is worth investigating what process opened it
- Randex is ancient by malware standards, but the port still appears in older threat databases as a flag
A suspicious open port is an invitation to look closer.
How to Check What's Listening
On Linux or macOS:
On Windows:
The process ID in the output can be matched against Task Manager or tasklist to identify what's actually running.
Why Unassigned (and Forgotten) Ports Matter
The registered port range has thousands of entries like port 3330: assigned to software that no longer ships, maintained by organizations that no longer exist, or simply abandoned after the initial registration. They aren't dangerous by themselves. But they're open territory.
Any application can claim an unassigned or forgotten registered port. Some do it legitimately by convention. Others do it because the number is arbitrary and they needed one. A few, like Randex, do it to blend into the background noise of network traffic.
The port number itself means nothing. What matters is what's behind it.
Frequently Asked Questions
Была ли эта страница полезной?