A tiny little Windows .exe file that would produce a cartoon sheep near the top of the screen. If the sheep appeared on the top edge of a window frame (like the File Manager or a word processing document for example) then the sheep would slowly progress along the frame grazing on digital grass. Until it reached the edge & fell off, at which point it would bleat in surprise & terror. Until it either hit the top of another frame to repeat the cycle, or fell off the screen entirely to reappear somewhere at the top again.
This was amusing if launched in the single digit instances, annoying if launched in the tens, & would bring a server to it's knees if spawned by the hundreds.
The sales manager of my employer at the time had started his life as a sheep rancher & still kept a few on his home acreage, so I thought he might appreciate the joke.
Day one saw a single instance & he was surprised and delighted. Day two saw a second spawned; he was surprised, delighted, & even turned the sound up to laugh at the surprised "BAAAA!" as they fell off the frames. By day forty-two he was no longer amused as his computer was taking far too long to do even simple tasks. At about the six month mark he was probably about ready to throw his computer off the roof.
I walked by, admired the sheep, & asked him why he no longer enjoyed them. He told me in no uncertain terms he was sick & fekkin tired of bloody sheep. I told him to go to lunch & I'd see what I could do to rid his computer of the infestation. He was only all too happy to hit the pub to calm down.
I uninstalled all the copies, removed the script that cloned the .exe file & renamed it so to avoid obvious detection, and verified that his computer was back as it should be.
He comes back, turns his system on, & cries out in gratitude that I'm a bloody genius. He grabs me, drags me back across the street, & stands me a pint in gratitude. At which point I felt honour bound to explain my prank. I figured he'd kick my arse back to the office & deliver my head to the HR department. Instead he slaps me on the back & praises me for a prank well done.
"But if you do it again, mind, I'll chuck yer arse off the roof to act as a cushion for the computer I'll send down next, Mkay?"
I agreed not to do it (to him) again, clinked in toast, & enjoyed my pint.
Of course I should have known it was all too good to be true.
One of my coworkers found the original .exe, copied it to their own computer, and used it to infect the main server. A task set to spawn a new copy every five seconds until the task was killed. By which time there were *thousands* of sheep infesting the server screens & the machines unable to do much of anything at all. And whom had just admitted to having pulled that prank on the sales guy? Whom got blamed for the server prank? Yeah... Sigh.
I was frog marched into the server room & told by the regional VP to "fix yer shit or clean out yer desk". Since I knew the exact file size of the executable it was a simple task to do a global DIR to find them, move them to a temp folder, & make sure the server task manager no longer spawned fresh copies. Make sure no false posatives in the temp folder, delete the folder, & reboot. Prove to the VP that no more sheep would be grazing, try to explain that *I* hadn't done the server prank, but all that got was the VP making a very loud (Drill Sargent projecting bellow) announcement that "any more pranks gets the joker fired!"
I certainly didn't pull any further ones, and a Fiver found its way to my desk wrapped in an appollogy note "For the server stunt".
Still, I loved those little sheep. I just wish I could see to run them again & laugh at the baaa'ing little baa-aa-aa-astards. =-)