A couple of stories
Back in the days of DOS in the 90s our college got the FORM virus. I managed to get it on a floppy disk and take it home to play. While looking at it in a HEX editor and seeing the message it was supposed too (but never did all the years we had it) display, I managed to infect the boot sector of our home computer with it. Balls. System would no longer boot. Luckily had a bootable 5 1/4 floppy that I'd used for booting to be able to play Frontier: Elite II and used that to boot the PC daily instead. I guess the virus needed to load into memory from the boot sector of the HDD to be able to infect other floppies. Because despite the HDD being infected for over a year (never had the original Windows 3.1 disk so couldn't rebuild), no other floppy ever got infected with FORM.
And frying my family friends Commodore 64 is the second story. Late 80s early 90s. Would go round most weekends and play on it. Would even buy the odd magazine with a cover tape now and then just to play the demo on it (Operation Wolf was the only one I remember getting on a tape as a demo). We never had a Commodore so was the only place I could get the Commodore fix was at theirs, and of course seeing them in the local WHSmith.
He had discovered POKE commands this fateful day, you could use while a game was loading or playing to put in cheats. But, to get to the POKE you had to interrupt the game. This required careful jumping of the expansion board at the back of the Commodore (I don't remember the exact details). This would jump you out of the game, enter the POKE for your cheat then carry on. He was successful and as always because he was doing it, I wasn't paying attention to how it was done and what NOT to do. So when he said he was going out for a bit, I said I'd stay which they were fine with :). Left me to play on the Commodore. I then decided
"I'll do that POKE command." I knew nothing about computers back then. Blindly did the shorting of the expansion or cartridge slot without fully reading the guide and the Commodore turned off and wouldn't come back on.
Oh shit. Panic kicked in. I waited a bit then went to their backroom where his sister and mum where sat. Said I'd gotten bored of the Commodore so watched TV with them for a while. Then about an hour later I said I'd best head home. The short walk home I thought about what I'd done.
Later that day I got the call "Was the Commodore working when you left?"
"Erm, yes, yes it was" was my shameful reply.
He had to send it off to get repaired. I think he got it done for free because I think there were issues with some randomly frying back then without 12 year old boys trying to do POKE commands. But that could be a false memory to suppress my guilt.
It's been over 30 years since that day and I don't see them anymore but I've also never confessed to frying his Commodore 64.