Innocent fun with net send

beamed-xmas-treeBecause it is the holiday season and most of us have a straining year of hard work behind us, let me just tell you a little story with more fun than moral in it. The story really happened, but the circumstances and details are altered to protect the innocent.

The setup

Imagine a full day of boring training workshops with a dozen developers in one room, each sitting behind a computer and trying to mimic the tiresome click orgy the instructor presents. Between the developers, there is one web-designer, clearly distinguishable by looks and questions. The workshops drags on and on, until Marvin, the protagonist of our story, loses interest in the clicking and sets out to explore the computer and its possibilities. This all happens a decade ago, when terminal servers were still new and fancy and windows was an open book for those who could read it. The computers were installed by the workshop host and used with a guest login.

The exploration

Marvin notices that the IP address of every computer was written on the computer case. It was just a matter of inconspicuous looks to gather the addresses of the neighbouring machines. The next step was to open a command shell – which was available without any tricks – and try to net send a message to his own machine. Net send was essentially a system service that listened to network messages on a specific port and displayed them as a dialog. So if you’d net send a message to a computer, it would be displayed in a message box in the middle of the screen on top of all active windows with a caption identifying the sender. The user had to acknowledge the dialog by clicking the button to be able to proceed in his original windows. In summary, net send was the perfect remote distraction tool. And it worked: Marvin was able to message himself with net send. The terminal server even disguised the real sender by sending the message with its address instead of the guest machine’s. Now Marvin could anonymously open modal message boxes with a custom message on every computer in the room, given that he knew its address. The workshop promised to be fun again.

The first reaction

After making up some witty messages, Marvin collected all his mental willpower to act indifferent while slowly typing the first message to his neighbour. It just read “Harddisk error” and was only a test drive if he was able to pull this prank without bursting out in laughter or being identified as the source. If he could message his neighbour without him noticing, he could message everybody in the room. After the net send command was complete, Marvin paused a bit and used his little finger to tap enter on the numerical block of the keyboard, to not draw attention to his keyboard pattern. As soon as the command was acknowledged, his neighbour let out a muffled groan and clicked the message box away without even reading it.

The messages

After that, the messages were longer and more sophisticated. After the first few messages, Marvin guessed the pattern in which the IP addresses were located in the room and sent messages to nearly everybody else attending the workshop. Some messages read “Virus found! Need to manually reboot the computer.”, others “Keyboard error. Press Enter to continue.” and the like. The reactions from the developers in front of the machines were always the same: A fretful sound and an acknowledging click without the slightest hesistation. Nobody rebooted or checked the keyboard. The messages were just dismissed and immediately forgotten like a temporary annoyance. Even when the message grew as long as two full sentences, the recipient just clicked it away.

The highlight

During a short recess, Marvin planned the ultimate net send attack: a message on the presenter’s computer, precisely timed to fit the workshop content. He went to the instructor and asked some question while memorizing the IP address of the machine that was connected to the beamer. If he sends a message to this computer, it would be shown on the beamer to the whole audience and the instructor. He used the remaining recess time to formulate the perfect message. The lectures began again, everybody took their seat and concentrated on the topic again. A few minutes into the workshop, Marvin hit enter and the message box appeared on the wall:

Attention! The beamer is overheating. Only a few minutes left before critical temperature level is reached and shutdown is forced to prevent damage.

Everybody stopped and gasped while they finally read a message. Probably only missing the dialog title that clearly stated that the message came from the terminal server, the sole non-developer in the room, the web-designer, asked the one and only legitimate question: “How can the beamer send this message to the computer over the VGA cable?”

Only a split-second later, a developer answered with “there is a standard for that”. Another one chimed in: “your computer also knows which monitor is attached through that cable”. A third suggested a solution: “We might just turn it off a few minutes to cool down. It’ll be okay afterwards.” Clearly out of his comfort zone, the instructor decided: “No, we just had a recess and I’m behind schedule. We’ll see how long this beamer bears with us.”

The moral of the story

Surprisingly, the beamer lasted the whole rest of the day and many days afterwards, without any further hickups. One attendee of the workshop silently laughed for about an hour and the day went by a lot faster. But the most surprising thing was that the only person that grasped the real marvel of the situation was the person with the least technical knowledge in the room. All the seasoned developers missed every clue that there was something fishy with a beamer communicating with the computer over a VGA cable and opening dialog boxes on the computer (and not just in-picture). And nobody reads the text in a dialog box ever. Especially not the title bar!


Marvin wants to apologize to everybody he bothered during this workshop. It was a fun idea originating from boredom, but it turned into a fascinating techno-social experiment. He says he learnt a valueable lesson that day, even if he doesn’t remember any content of the training itself.

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