Three options come to mind.

A virus that adjusts your mouse sensitivity by like 5% every time you unlock your computer. Just enough that existing muscle memory is off, so you either have to adjust to the change or change it back every time.

A virus that installs and/or sets a similar but not quite right keyboard layout, and swaps to it randomly few boots. For example, setting the keyboard to Canadian Multilingual Standard instead of US English, where its only some of the punctuation keys that are changed.

A virus that randomly pops up a terminal window and outputs suspicious-looking text, and closes itself before the user has time to read it.

I did this in high school, it was just a basic script that spawned a warning dialog box (the kind thats always on top) that just said you can’t close this, part of the script action was making tge task scheduler check every few seconds if the script was running… If it wasn’t then run it.

Since I was making the task scheduler do the checking it meant even if you tried to task manager force close the script it would just open again in a few seconds, it was not a permanent task it was a temporary one and every opening of the script would reset that task so basically the only way to get rid of it was to restart the computer as that would clear the task.

There’s a 1 in 50 chance that any copy text command cuts the text instead, and vice-versa.

back when I was in school someone wrote a script that just openened the optical drive at random intervals and put it in the Autostart of every PC in the Comouter room

I wrote a simple script once that ran in the background and all it did was toggle the state of the caps lock key every 30 minutes. I set it up on a co-worker’s computer as a scheduled task for an April Fools prank one year. I thought for sure he’d figure it out pretty quickly, but by mid-day, he had completely disassembled his keyboard, convinced the button was getting stuck due to gunk buildup. Eventually I ended up just disabling the task so he thought he had managed to fix it himself.

I had a friend who sent me a “Y2K fix” program back in '99. Said it would patch the error so I’d be safe. When I ran it, it swapped the letters Y and K on my keyboard.

On somethingawful back in the day if you were on any one page on their forums for more then about 20 minutes, a audio clip would play that said something like “HEY EVERYBODY I’M LOOKING AT GAY PORNO”

Simple, every now and again switch a key input with a neighboring key. Imagine slowly losing your confidence in your motor skills as you just can’t seem to type properly no matter how careful you are.

It would do it like once every 10-1000 minutes, you will never catch it and slowly lose your grip on reality.

In my highschool programming class we made a TSR (in Borland pascal) that would change every 15th keypress to an “e”. It wasn’t self propagating, so it wasn’t a virus per day, but it was highly annoying. It survived on memory after the netware logoff, and you could only get rid of it by rebooting.

We also had these everex brand 286 or 386 computers… They had a little LCD screen that would read out what sector/track was being read on the disk. We found the memory address (80h) where we could write arbitrary text to the LCD. That was fun.

There was a guy in my dorm who really didn’t like his roommate. Really, really didn’t like him. This was in the early aughts.

So one day he goes on his roommate’s computer and puts a text file in his startup folder. The file says, “Your computer has been infected by the Snood virus!”

For context, Snood was a free video game people downloaded in the early aughts. Basically the same as Bust-A-Move, which probably doesn’t clarify anything if you didn’t already know what Snood is.

Anyway: “Your computer has been infected by the Snood virus! If you don’t score [extremely difficult but not completely unrealistic high score] points, all of your files will be deleted!”

He laughed to himself and promptly forgot about it.

Weeks later, the roommate is on his computer in the middle of the night.

“What are you doing up? Go to bed.”

“I can’t. It’s this stupid Snood virus.”

When I was in high school in the 90s a group of us in computer class made a ‘virus’ that would launch the hamster dance website in all of the classroom computers randomly. We had to put it on a diskette and install it manually on each computer but at the time none of the computers even had antivirus so the school had to reformat them to remove it.

Uhh, it was “Hey everybody, I’m looking at gay porno!” and then it proceeded to spawn hundreds of internet exploder windows pointing at goatse.cx. Thank God I was at home, alone, when it got me.

I had a boss that wasn’t exactly technical. I wrote a power shell program that would randomly every 5-30 minutes give a pop-up that said “good job”, which he always said regardless of what was going on. Placed it in his startup folder on his machine. I thought he would figure it out and tell me to knock it off… Well I forgot about it, 9 months later during my annual performance review it popped up while I was looking at his screen. He apologized and just alt tabbed it away.

I offered to take a look and see if I couldn’t stop it, and he said yes and then walked away to take a break. I then deleted the script I put on there. He gave me extra performance points (meaning a higher pay raise.)

I call bullshit. In the 90s you had to turn a phisical wheel to increase the volume of the computer.

I don’t remember the details but my mom’s first cousin called me once to fix her computer when I was a teenager.

No matter what she typed it came out as, “I AM FUCKING GAY!”

Seems like all I had to do was type “stop”.