Back in mid 90's, as a fresh student barely having a year of programming under my belt but with a burning passion I was doing my summer practice (required by school) to a factory IT center. This factory was making a lot of large industrial stuff but during that period the current contract was to make propellers for big ships. Like 20m high one. And they used AutoCAD in the IT center to design those. For a Japanese client.

So the director of said IT center, seeing me how I dabbled in all kind of stuff with latest and greatest technology asks me "can you create a copy protection?". Nowadays I see this kind of question as a job on my freelancer marketplace and I always say to the potential customer "impossible, and if anyone else says otherwise are either incompetent or just want to hustle your money" but back then? my naive brain said "sure I can".

The IT center just acquired, at around 4000 USD each, a brand new line of 486 DX2 at a whooping 100 MHz which came with latest and greatest Windows 3.1 for Workgroups. Around 20 of them for all their design engineers to use ACAD at a faster pace. Serious business required serious tools. So I enter the scene with my protection. Which was a wrapper around the protected "exe" that on launch would ask for password, 3 tries and you're out. If password was provided then it would unwrap the good exe and launch it, otherwise the protection would kick in.

And oh boy, what a marvelous protection I wrote. First step - overwrite MBR with zeroes, you can guess to what goal.
Second step - well, this one is a bit complex. You see back then you could directly access graphic cards DMA channel and write your own graphic driver inside your application because, well, DOS was like that. And poor Win 3.1 was no different either. And because of a physical layout that majority of board back then employed all the same you had an electrolytic capacitor near (like 2 mm only) a pin. Which said pin could go to up 25 KV if you were driving a certain pattern on your graphic card. Which would result in a shortcut between the pin and the capacitor. Which would ignite the resin that was there. Which would set your computer on fire.
Third step - restart the PC.

So I am there with the director, head of designers and a bunch of other people to test my copy protection. I explain to them in what the protection consist of, and we test it. They wanted to test it on "acad.exe", so I wrap it up in my protection, delete the original and the new exe is launched. All good, password prompt, get in, Autocad is launched, they can do the work in peace. Except the director asks "and if I launch this wrapper tool separately, what happens?". "Nothing, it's just a tool and if you don't supply a parameter will simply exit". So the director does that, except he supplies a bogus parameter, by mistake, and not any parameter but ^U...you know, the combination that a Windows user will see at a command prompt when he does a mistake and presses CTRL+Z (Undo in Windows), because he pressed space and then wanted to back it off..and muscle memory for that action is CTRL+Z. And happily my tool tries to wrap around a file called ^U, but for some reason that file instead to be "not found", because I had this coded, was treated at "launch the protection". So here a little bug, launched my protection on a $4000 brand new machine. Of course MBR was zeroed instantly and then we see some stuff scrambled on the screen (protection no 2) and puff!! we're at BIOS reset. No fire!!! Why? because protection no 2 should've run for 10 seconds to allow the buildup of those 25 KV, but I was lucky because my dead ass brain introduced another bug and I was triggering the reset immediately.

I spent the next 3 days, me and the head of designers, rewriting the MBR by copy/paste via eyes and hands, using a hexeditor, by reading the MBR from another 486, and I was lucky since they all had identical configuration. That protection scared off the director, he never use it. And my ass hurt from the stick because $4000 during that time would've been both my parent income for an entire year.