That lesson? Some IT departments (not 404 Tech Support) are willing to fry lots of equipment and waste company dollars to teach you to not just connect whatever piece of equipment you want to the network.
What happens when you cross a computer power cable with an ethernet cable? When you plug them both in, you have 110 volts being delivered to the network jack thanks to the Etherkiller. Sizzling RJ-45!
It all started one day with this guy, the original [sic] Etherkiller, developed with a few misc parts to warn new users that the IT department is not to be messed with. You too can make one at home, connect the transmit pins of the RJ-45 to HOT on 110VAC and the receive pins to Common. Modify to suit, taze by varying pinout.
This led to some general discussion that this particular device really is in a class of devices, now called the “killers”, which need to be made.
They have whipped up the same thing for VGA cables, IDE cables, and a bunch of other interfaces. You can see them at http://www.fiftythree.org/etherkiller/
Don’t mess with that IT department. Lesson learned! Also, don’t try this at home.