Port 663 sits in the well-known ports range (0-1023), officially assigned by IANA to a service called "PureNoise." Both TCP and UDP port 663 carry this assignment. The software it was meant for is a relic of 1990s encryption ambitions—still registered, rarely used, largely forgotten.
What PureNoise Was
PureNoise was encryption software developed by PureNoise Ltd in the mid-to-late 1990s. The company described it as "military grade chat encryption" designed to protect private communications. Their slogan: "Strong Encryption Made Fun."1
The software aimed to make privacy protection accessible. Users could hide their messages in what the company called "Pure Noise"—encrypted chat that looked like random data to anyone intercepting it. The system used AES (Advanced Encryption Standard) encryption and invited cryptographers to review their implementation.1
PureNoise was developed during the Crypto Wars era, when encryption software faced export restrictions in many countries. The company emphasized that their software was "legal to use in any country in the world" and had been "exported from a country with no encryption export limitations."1
The vision was ahead of its time. Secure messaging. End-to-end encryption. Privacy by default. These ideas would eventually win—but PureNoise wasn't the software that made it happen.
Why Port 663 Exists
When PureNoise Ltd requested a port assignment from IANA in the 1990s, they got one. Port 663 became the official home for PureNoise chat traffic. Both TCP and UDP were assigned, giving the protocol flexibility for different types of communication.2
The port remains officially registered to this day. IANA doesn't routinely clean up old assignments. Once a port is claimed, it tends to stay claimed—even when the service it was meant for disappears.
What Happened to PureNoise
The software never achieved widespread adoption. While PureNoise Ltd maintained their website and offered downloads through the late 1990s and early 2000s, the service failed to gain the critical mass needed to survive.
By the mid-2000s, other solutions had taken over. PGP for email. OTR (Off-the-Record) for instant messaging. Later, Signal, WhatsApp, and other modern encrypted messaging apps would dominate the space PureNoise had tried to occupy.
Today, purenoise.com still exists as a dormant website. The software is no longer actively developed or supported. The company appears to have ceased operations years ago.
The Reality of Port 663 Today
Port 663 is essentially unused. Network scans show minimal activity. Security databases list it as "not associated with any virus or Trojan"—which tells you how irrelevant it has become. Even malware authors don't bother with it.3
When you check what's listening on port 663 on a typical system, you'll find nothing. No service. No process. Just an empty port with an official assignment that nobody uses anymore.
This is common in the well-known ports range. Many early Internet services claimed ports in the 1980s and 1990s. Some thrived. Many didn't. The ports remain assigned, permanent markers of protocols that came and went.
What This Tells Us About Port Assignments
Port 663 is a reminder that IANA assignments are more permanent than the services they're assigned to. The registry is archaeological. You can read through it and find the entire history of networked computing—the successes, the failures, the experiments that went nowhere.
Some ports carry the entire weight of the modern Internet. Port 80. Port 443. Port 22. These ports matter. Traffic flows through them constantly.
Other ports are fossils. Port 663 is one of them. Officially assigned. Technically reserved. Practically abandoned.
The well-known ports range wasn't designed to be cleaned up. It was designed to prevent conflicts. As long as nobody else tries to use port 663 for something different, PureNoise's assignment doesn't hurt anything. It just sits there, a small footnote in the history of encryption software.
How to Check What's Using Port 663
Even though port 663 is rarely used, you can check if anything on your system is listening on it:
Linux/macOS:
Windows:
If you find something listening on port 663, it's worth investigating—because it almost certainly isn't PureNoise.
The Well-Known Ports Range
Port 663 belongs to the well-known ports range (0-1023), sometimes called the system ports. These ports are assigned by IANA and typically require root or administrator privileges to bind to on Unix-like systems.
Being in this range means port 663 was considered important enough to warrant official assignment when PureNoise Ltd requested it. The bar for getting a well-known port assignment was lower in the 1990s than it is today. Many ports in this range were claimed by services that never achieved widespread use.
The registry is permanent. The services are not.
Related Ports
Other ports from the same era that share similar stories:
- Port 657: IBM RMC (still used in some IBM environments)
- Port 666: Doom multiplayer (ID Software's game from 1993)
- Port 674: ACAP (Application Configuration Access Protocol, largely obsolete)
Some of these ports found second lives with different services. Others, like 663, remain tied to their original assignments—ghosts in the registry.
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