Decade or so ago, logging into a work computer and suddenly the screen is just tiled with the word "virus", but a bit janky looking like it was a screenshot of the word that was enlarged and tiled with no thought to whether the right side of the image lined up with the left and such - it was a very 90s cheesy movie like depiction of what happens to your comp when you get a virus, like you'd expect the next scene to be some shady hacker on the other end exclaiming "I'm in!"
Then again, I don't know jack fuck about viruses, and the machine is behaving super weird, so I unplugged the internet cable from the back, and called my manager over. He had a similar "...is this for fuckin real?" reaction that I did. Mind you, this is a hospital, so if one of our computers is fucked, this is a big deal for potentially leaking patient info, so even though it had that kind of slapstick appearance, no one was fucking around with it: so, manager pushed it up the chain, and after a few mins a fucking SWAT team of IT guys comes in and starts doing their own assessment.
After some deliberation, they start troubleshooting - keystrokes and whatnot don't seem to be responsive. One of them eventually reaches back behind the monitor and 'poof' the screen pops back to the normal login screen.
So, that facility had a fancy custom login screen, which was some generic desktop background type scenery and a wall of text that none of us ever put any thought into. One of the snipits on that wall of text was instructions on what to do if you suspect your machine has virus (which was basically what I did - leave it running, unplug it from the internet, and call IT... hooray, I'm not completely stupid!). What ended up being the cause of the "virus" tiling was the fucking VGA cable slowing worming its way out of the back of the monitor - when I got to it, that thing was hanging on by a thread, and touching the desk it was on was just enough of a bump to make it cross that line between having enough of a connection to do its job vs not. That micrometer of pull of on that cable wasn't enough to completely cut its signal, but it wasn't enough to produce a normal display either: it just picked a random spot on the screen, and filled the monitor with that repeating image. The spot it just happened to do this to was the word "virus" in the custom login text explaining what to do if you think you have a virus, lol.
TLDR, got my management chain from my dept to the top dogs running the hospital, and the entire fucking IT department to swarm to my unit over a potential data breach that ended up being a wiggly VGA cable.
Whoops.
