Port 1520 sits in the IANA registry with an official assignment: atm-zip-office (ATM Zip Office). Both TCP and UDP. Registered to someone named Wilson Kwan.1
And that's where the trail goes cold.
What We Know (Almost Nothing)
There's no RFC for ATM Zip Office. No protocol specification. No company website. No archive of documentation explaining what this service was supposed to do. The name suggests something related to ATM (Asynchronous Transfer Mode) networking and file compression or transfer, but that's speculation built on two words and a hyphen.
Port 1520 exists in the registered ports range (1024-49151)—the space where IANA assigns ports to specific services upon request. Someone applied for this port. Someone had a protocol. Someone needed the Internet to recognize this number.
And then they disappeared.
What the Port Range Means
Ports are divided into three ranges:
- Well-known ports (0-1023): Reserved for core Internet services like HTTP (80), HTTPS (443), SSH (22)
- Registered ports (1024-49151): Assigned by IANA to specific services upon request—this is where port 1520 lives
- Dynamic/ephemeral ports (49152-65535): Used temporarily by client applications
Port 1520 isn't reserved for a fundamental Internet service. It's registered for a specific application that presumably existed at some point. The registration means someone formally requested this port number, described their protocol, and IANA approved it.
Then the protocol vanished.
The Security Shadow
Port 1520 appears in old trojan port lists with vague warnings that "a virus has used this port."2 No specific trojan name. No timeline. Just a flag in a database somewhere suggesting that at some point, malware exploited this forgotten port.
This is common with obscure registered ports. If nobody's actually using port 1520 for its intended purpose, an attacker might use it precisely because it won't trigger immediate suspicion. An open port 80 means a web server. An open port 22 means SSH. An open port 1520 means... ATM Zip Office? What's that?
That confusion is useful if you're hiding.
Checking What's Listening
If you want to see whether anything on your system is using port 1520:
On Linux/Mac:
On Windows:
If you see something listening on port 1520 and you don't recognize it, investigate. It's unlikely to be legitimate ATM Zip Office software (because we can't find evidence that exists). It's more likely to be:
- Custom internal software someone configured to use this port
- A service that chose an obscure port to avoid conflicts
- Something you should investigate further
Why Ghost Ports Matter
The Internet is full of ghost ports like 1520. Protocols that were registered, possibly implemented, possibly used by a few hundred or thousand people, and then abandoned as technology moved on.
These aren't mistakes. They're archaeological artifacts. Port 1520 tells us that in some moment in Internet history, someone built something they believed was important enough to register a port number. They went through the IANA process. They documented their protocol somewhere, even if we can't find it now.
And then the world moved on without them.
The Internet remembers their port number. But it forgot their protocol.
That's both melancholy and beautiful. The infrastructure preserves the space—port 1520 still exists, still reserved, still assigned to atm-zip-office in the registry. But the meaning is gone. It's a door with no room behind it. A phone number for a disconnected line.
What to Do with Port 1520
Unless you specifically know you're running something that uses port 1520:
- Don't open it in your firewall—there's no standard service you need to access here
- Block it at the perimeter—if you're running a network, there's no reason to allow traffic on this port from the Internet
- Investigate if you see it listening—because it probably shouldn't be
If you're a developer choosing a port for a custom application, you could technically use 1520. It's registered, but to a service that doesn't seem to exist anymore. Whether that's respectful to the ghost or pragmatic reuse of abandoned space is a question of philosophy.
Related Ports
Other ports in the ATM-related registered range include:
- Port 1516: VPAD (Virtual Private ATM Data)
- Port 1521: Oracle database (nCube License Manager)
- Port 1525: Prospero Directory Service
Most of these carry similar stories—officially registered, minimally documented, rarely used in the modern Internet.
Frequently Asked Questions About Port 1520
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