What This Port Is
Port 1042 lives in the registered port range (1024-49151), which means it had to be officially requested and assigned by IANA. Unlike the well-known ports (0-1023) that you hear about—SSH, HTTP, SMTP—registered ports are for everyone else. If you're building a custom service, you ask IANA for permission to use one.
Port 1042's official assignment: afrog, a protocol for Subnet Roaming. This was probably someone's idea for a helpful local network messenger. The application runs on both TCP and UDP, leaving both doors open.
It never became popular. Nobody runs afrog anymore. The Internet forgot about it.
But something else remembered.
The Trojan Problem
The BLA trojan claimed port 1042 in the 1990s. This wasn't coincidence—malware often picks less-known ports, betting security teams won't be watching. BLA was an anti-protection trojan designed for Windows 95 and 98. It offered remote access, keylogging, password theft, and proxy functionality. Everything an attacker in the late-90s could want.
It worked. People found their machines compromised, their passwords gone, and someone else controlling their keyboard from a thousand miles away. Port 1042 was the door.
The trojan earned aliases: "Asian trojan," "Backdoor.TrojanSimovits." Different names, same outcome. If you saw port 1042 open in the 90s, you had a serious problem.
Why This Matters for Your Network
Port 1042 should be closed on your machine. If you find it open, something is listening, and it's almost certainly not afrog.
To check if port 1042 is open:
On macOS or Linux:
On Windows:
If nothing's listening, you're fine. If something is, identify it immediately. Check what process owns it, whether it was installed intentionally, and whether it has automatic startup enabled.
The Unassigned Port Principle
Port 1042 teaches an important lesson about how ports work. IANA's registry doesn't police enforcement. There's no mechanism that says "only afrog can use port 1042." The registry is a phone book, not a bouncer. When you open a port, anyone can answer.
Legitimate services can listen on port 1042. Custom applications. Internal tools. But so can trojans, worms, and backdoors. The port doesn't know the difference.
The fact that port 1042 was hijacked by malware decades ago shows that ports themselves are just numbers—they're only as safe as the systems and administrators protecting them. A trojan that worked in 1998 wouldn't work on a modern machine with modern defenses, but the principle holds: unused registered ports are valuable real estate for attackers.
Why Unassigned Ports Exist
The 65,535 TCP and UDP ports represent the entire address space for network services. Out of that, fewer than 200 are truly "well-known"—the essential infrastructure (DNS, HTTP, SMTP, SSH). The remaining 65,000+ ports exist for every custom application, private service, and specialized protocol anyone can imagine.
Port 1042 was assigned to someone's idea. That idea never took off. The port stayed in the registry, dormant, until the BLA trojan found it useful.
This is why port scanners exist. This is why network administrators monitor which ports are open on their machines. The unassigned ports are a vast, mostly silent corner of the Internet. Most of them carry nothing. But the ones that do carry something—you need to know what.
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