Port 1616 sits in the registered ports range (1024-49151), officially assigned to the NetBill Product Server. If you've never heard of NetBill, that's because it died before most of today's Internet users were born.
What NetBill Was
NetBill was Carnegie Mellon University's answer to a problem that seemed critical in the mid-1990s: how do you buy digital goods online without getting ripped off?1
The system handled micropayments—transactions worth pennies or dollars—for things like downloading articles, software, or digital content. The protocol promised something remarkable for its time: you only paid if you actually received the goods intact.2
It worked through encryption. The merchant would send you the file encrypted, withhold the decryption key, and only release it once payment cleared through NetBill's transaction server. Atomic delivery: either both sides got what they wanted, or neither did.
The transaction cost was about 1 cent for a 10 cent item. That efficiency mattered when credit card fees made small purchases impossible.
What Happened
NetBill was presented at the First USENIX Workshop on Electronic Commerce in July 1995.3 Two years later, CyberCash absorbed it. Then PayPal came along and changed everything about how online payments worked. NetBill's careful protocol for certified delivery of encrypted digital goods became irrelevant when people just wanted to send money to an email address.
PayPal eventually absorbed CyberCash. NetBill became a footnote.
What Port 1616 Means Today
If you scan port 1616 on a modern system, you'll almost certainly find nothing listening. The port remains registered in IANA's database—a permanent record of a protocol that seemed important enough to deserve official recognition.
This is what happens to ports when the services they were assigned to disappear. The number doesn't get recycled. It just sits there, empty, a reminder that the Internet's infrastructure carries the ghosts of every protocol that tried and failed to predict the future.
The Registered Ports Range
Port 1616 belongs to the registered ports (1024-49151). These are assigned by IANA to specific services upon application. Unlike well-known ports (0-1023), registered ports don't require administrator privileges to use on most systems.
Anyone could, in theory, run a service on port 1616 today. But they'd be squatting in NetBill's old address. The official assignment still says "NetBill Product Server," even though no NetBill servers exist anymore.
How to Check What's Using Port 1616
On Linux or macOS:
On Windows:
You're looking for something listening on this port. Most likely, you'll find nothing. But if something is there, it's not NetBill—it's either a modern application that chose this port arbitrarily, or someone who didn't know this number was already spoken for.
Why Empty Ports Matter
The Internet is built on a finite resource: 65,535 port numbers. Some are in constant use (80, 443, 22). Others, like 1616, are assigned but abandoned.
These empty ports tell the story of how the Internet evolved. Every registered port was someone's attempt to solve a real problem. NetBill tried to make micropayments work in 1995. The protocol failed, but the port number remains—evidence that the problem was real, even if this particular solution wasn't the one that survived.
The port registry isn't just a list of what works today. It's a historical record of what people thought would matter. Port 1616 is a monument to the idea that buying a newspaper article for three cents online would be important enough to need its own protocol and port number.
They were right about the problem. They just didn't predict that the solution would look like PayPal, not NetBill.
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