I don't remember messing with the computers thenselves, but I do remember my friends and I finding the password to the public wifi and connecting to it for all of like a day (w/ a VPN so as to not get caught) before getting booted off and the password reset. Rinse and releat a couple times before we couldn't crack it anymore

So many comments are about such major things, where as at most I only really put ThePowderToy into the shared drive for student accounts in my junior year of highschool and once in my freshman year made a simple batch program that all it did was constantly open up command prompts but didn't do anything harmful.

Y'all did so much more interesting and worse things than I did, I swear

Idk how much it's really messing with the computers, but once during a standardised maths exam where everything was supposed to be locked down oh all the computers (including preventing you from accessing the calculator), I figured out how to get around that and open the calculator (can't remember exactly how), but anyway I was good at maths so I didn't need it and I thought it would be funny to point it out to the teacher watching over the exam and I got accused of cheating so that was fun

ITT: people admitting to violations of 18 USC 1030, which is a terrible law that is way too vague.

SubSeven

One time we got around the security for a shared windows folder (Win98). Another time a couple of us printed fake midterms for ourselves on official headered paper. But the one that sticks out is this trojan program I got from my older brother called deepthroat. I put it on a couple of other people's computers that I wanted to mess with, and proceeded to open their cd tray, pop up fake warnings/errors, and other random stuff that a friend and I thought was hilarious at the time. It all stopped when I popped up a message that said "Contacting [name]'s parents..." on this girls computer and she got the teacher's attention about it. He knew what was up and scanned all the computers. He was mad but we didn't really get in trouble. We also did the fake desktop screenshot stuff :D

Back in the day keyboard and mouse were connected to the back of the computer with identical (but color coded) PS-2 plugs.

Today one would expect that swapping two mechanically identical plugs would result in no major trouble - think USB - but back then COLOR CODES HAD TO BE OBEYED!

Or computer science teacher came to help when our PC won't boot up, tried reset, tried reset again, fiddled with the BIOS, gave up.

That wasted more than halve the lesson's time just for us to swap plugs back to working while he wasn't watching.

Sometimes things simply don't work when the teacher is around...

Nothing crazy or software related, but screwing with people with a wireless mouse with one of those tiny receivers is pretty funny.

For 5th and 6th period in middle school, in the early 90s, I was in the same lab and had complete access to the computers. Rather, I was in charge of them. I was a TA for one period and it was a free elective for another period. I don't remember the details...but somehow I was there for both periods every day.

The teacher who ran the lab just left it all up to me. So, I installed games on all of the computers. Oregon Trail, DOOM, and Q*bert were the three that I remember.

Students would be sent up to the computer lab, on a daily basis for both periods. A lot of times the teacher who ran it would go run errands since I had it covered. When those kids came up, the entire lab just played games.

Also, since it was 6th period, I'd have the honor of shutting down the entire school network and systems at the end of the day. I'd get to call teachers and tell them to get off so I could shut it down. Some times I wouldn't contact them, and I'd just kick them off the network and shut down anyway.

It was a fun time.

I was in our schools computer service team and they trusted the (competent) students way too much. I never misused those credentials but thinking about it now I could have done some hilarious stuff... Anyway. Even without too many permissions I did a thing or two to the computers. I once realised no computer had the BIOS password set. So I set one on a library computer to reserve it for me. Another time i realised you could take the whole network down if you connected two LAN ports directly with each other. That one was more on accident.

I remember dialing into the college network during the summer to access Usenet and play muds. It was some kind unsecured number, I forget how I found it

I used to fuck around with desktop shortcuts for fun. For example, replacing the internet browser shortcut with a shortcut to a script that starts the browser, but also does other weird stuff, often only after a certain time.

So somebody would "start the browser" and every 30 seconds, the script would open another browser window, or word, or close a browser window, or shut down the computer, etc.

I thought it was just harmless fun that was easy to fix and figure out, but the school IT would look everywhere to fix the strange issues and believed that students had installed a "hacked version" of firefox..

We had typing as a class, oriented toward business typing proficiency, words per minute, that kind of thing. This was running on PCs with DOS running WordPerfect 5.1

They were all running some network software (netware) so the teacher could see screens and things. There wasn't a school wide network at the time, but I remember finding out how to send messages that would pop up on the bottom line of the screen of one or all the computers. .

We all had laptops in highschool, and apparently our IT admin couldn't figure out how to disable the "Upgrade to windows 10 for free!" Popup everyone was getting. Anyone that upgraded to windows 10 got called down to IT had their laptop reimaged. When I heard about it, I figured that they must have been checking OS by our user agent or some other web-based method, as upgrading to windows 10 appeared to kill all of the group policy things. Assuming they had everyone's mac address recorded, you could correlate laptop to user pretty easily.

From then on, every week I would USB boot a different OS. Linux, Solaris, FreeBSD, Windows 10, Windows XP, etc. I would run each OS for a few days until I got called down to IT, had my laptop inspected, and sent back to class when everything checked out. Drove them nuts, I thought it was funny.

On a school Mac I figured out using some command I could create a new admin account. I used this account to gain access to the school WiFi password and admin account password. I found out what a vpn was and brought my own laptop to us instead of the crappy ASUS Eee PC netbooks. The Vice Principal was not happy. They called my parents for a meeting ( I had a lot of issues with many IEP meetings). My parents were okay with it.

We would also pass around pirated GTA 3, GTA Vice City, Free versions of Minecraft, and Halo CE and run them off of USBs.

Background on a lab to a high resolution naked mole rat picture zoomed in so it kinda looked like a scrotum maybe, but it wasn't: It was just a naked mole rat.

Kept removing the web filter proxy from all the browser settings lol the it guy got pissed all the time but didn’t have a way to stop us

would put portable games on the public network share, apparently they didn't have logs of people putting stuff there

we installed Duke Nukem 3D on all of the computer lab pc's

.bat files to open meatspin until explorer crashed Setting tasks to open a video file on login

I was in a programming class in the 9th grade in which we were taught Visual Basic. I found out that you can run other executable from applications written in Visual Basic using the Shell command and that this bypassed whatever restrictions they had placed on our computers. I could open any Windows XP (I think?) admin utility this way. But more noticeably, I could open the previously disallowed crappy space pinball game. I showed this to some of my friends, and they did the same. A few days later, some of them are suspended for, no shit, "hacking," because they were caught playing pinball. Not me, though. I kinda resented that.

Oh, I also did an infinite loop with the "Beep" command in it and this caused my computer to bluescreen and not come back.

The term "Xennial" always resonated with me. We were the ones that were on the cusp of the ending of the Gen X era and the beginning of the the Millenial era. Also 1979 here.

Dropped some extensions on the Mac image servers, toyed with Next machines, all kinds of shenanigans.

We never had school computers :(

I had GLTron and Pocket Tanks installed on a flash drive, so my friends and I would just play games whenever we had free time.
I also found a couple fun network based utilities in Windows, and all the computers in the district were on the same network. I was messing with NetSpend one day and managed to accidentally send a message to every computer in the school, which then all promptly crashed for some reason.
I also had fun messing with the netchat application. My mom worked at another school in the district, and one time I arranged for her to open netchat at a specific time while I was in computer lab, so I could connect to her computer from a lab computer and we could chat back and forth.

In 9th grade (1984), I had a typing class using IBM PC Jrs. I made a quick and very simple breakout game in BASIC one period and distributed to the rest of the class.