During my training, ~2004, I managed to kill the TCP/IP stack on an IBM mainframe running z/OS by accidentally creating a fork bomb with a perl script meant to

During my training, ~2004, I managed to kill the TCP/IP stack on an IBM mainframe running z/OS by accidentally creating a fork bomb with a perl script meant to test the performance of the newly installed BIND9. Fortunately, it was on a testing system, SNA continued to work, and the system was due to be rebooted on the weekend anyway, so it was not that bad. Not myself, but a few years ago, a new coworker managed to accidentally delete all user accounts from our Windows domain while trying to "clean up" the Group Policies. Our backup solution, while working, was rather crappy, so we had to restore the entire domain controller (there only was the one), which took all day, even though it was not that big. Fortunately, most users took it rather well and decided to either take the day off (it was a Friday) or tidy up their desks and sort through the papers they had lying around. A few actually thanked us for giving them the opportunity to "actually get some work done".