Where do I start...
My first proper job, not counting work experience during high school, was very late '70s to very early '80s. Working for a company that designed and built a S-100 computer. At one stage we had sold one of those computers to the company that ran the catering and housing for a mine site that was under construction. I got to live on site for a while, programming that computer, and then the second computer they bought.
At one stage they added some fancy security locks, two to keep the case locked, and eight front panel key switches to unlock various functions depending on what key you had. Some sort of unusual geometry of the keys, I think it was sorta 3D triangles or some such. Supposedly unpickable. So one day, I'm twiddling my thumbs while I wait for a compile, I have a medium sized screwdriver, and a gleam in my eye. I love a challenge. Stop me if you've heard this one before. Didn't take long to "pick" one of the case locks open, which was just shove the screwdriver in and jiggle it randomly a bit, barely any force needed. Close it up again, go get one of the bosses, demonstrate it to him.
Since the office computers where being used during business hours, I was often working on them during the night. Remember, this was early '80s, computers where rare. Since I was in the office of all night anyway, the client slung me a bit of extra cash to be the emergency accommodation officer. Late arrivals needing to sign in and get their rooms assigned, drunks coming home from the pub but lost their key so I had to cut them a new key, that sort of thing. The main accommodation was demountables with small rooms and cheap locks. Aluminium keys that would break off leaving half of it inside the lock, locks that would rust in the high tropical humidity and jam, etc. I became adept at pulling the pin out of hinges and opening the doors the other way, using needle nose pliers to grab the half key stuck in the lock and giving them a twist, and for those really hard cases, using a crowbar to break the seal on the windows and open them up, without actually breaking the windows. I've lost count of the number of places I have legally "broken and entered".
My next job was with the Department of Health. Usually I was in the IT offices, but once I had to go out to the head office, where they actually used the systems we developed. I should point out that up to that point, I had nothing to do with the IT security systems. For some reason or another I was in need of a real password to log onto some part of the system to check what ever they had sent me out to fix, something to do with patient records or billing I think. I didn't have a suitable real password, I only knew the test passwords. While someone went off to find a password for me, I pushed the return key for some reason. Once again, stop me if you've heard this one before. "Password" accepted, I was in. Repeat a few more times just to double check, indeed leaving the password field blank got past the password check. I reported this, and they asked me to fix it when I got back to my office.
Slightly off topic, but it did involve bypassing a security mechanism. At around about that time I had a game for my very own computer, on a floppy disk. It used the sort of copy protect mechanism where they use a laser to burn coded spots in the floppy disk. The idea is you write to those spots, of your can't read back what you wrote, the proper holes where in the disk, copy protection was in place, continue to boot the game. Naturally at some point the copy protection code managed to write to the wrong bits of disk, corrupting it so it would no longer boot. I'd paid good money for this game, and as state above, I love a challenge. Didn't take long at all to disassemble the boot code, find the call to the copy protection code, simply patch out the call, and boot my game. It was the copy protection code itself that had been corrupted. Some of the graphics had also been corrupted slightly, but it was still playable.
I'll stop now, the beginning of this comment is about to scroll off the top of my screen.