There's a MUD I used to be into back in the day (it's actually still online, and my characters still exist!), and I got several of my friends into it. Unfortunately, most of us didn't have internet at home and could only play it in the school lab.
This was a fairly rural area, and it was the mid 90s. CompuServe and AOL existed, but local access numbers did not - long distance was still quite expensive, and internet time was strictly monitored and enforced even if you were using your infinite free hours on your 12th AOL screen name.
In about '97, a local ISP set up a dial-up point of presence in our town, so the long distance problems were solved. Whoo! However, some of my friends had parents who weren't on board with this whole "internet fad" and so remained offline.
Little shit that I was, I figured out that if you used a terminal client to dial the ISP's number instead of the dial-up networking client, you'd land in a shell; that typically wasn't supposed to happen. Hmmm.....
Normally that console shouldn't even be accessible via the customer dial-up number, but it gets better. You didn't have to authenticate to access that shell, either; just dial the number, wait about 5 seconds after the handshake completes (it's expecting you to start a PPP session at that point), and bam, you land in a shell. From that shell, you could telnet to anywhere on the internet, including the MUD server.
I'm not exactly sure what piece of telecom equipment acted as our game server for so many years, but I want to say it was the router connected to the modem bank. Whatever it was, it was misconfigured in a very advantageous way.
Once I figured that out, the six friends I'd gotten into that MUD were all set as well as a few more people they brought in. HyperTerminal was no zMUD for sure, but it was better than not playing at all.
Looking back, I kinda feel like an ass now. That modem bank was fed by two T1s, one for the modems, and one for the data backhaul, and could support up to 24 simultaneous connections.
It was very common to get the "all circuits are busy now" error message on most days. Making things worse, almost half of the total capacity was us playing MUDs without even being subscribers to the ISP (well, I was, but still).
That worked up until about 2002 when that small ISP was bought out by the local telco who apparently had their equipment configured correctly.
