I had this happen to me! I created an instance for myself and a few friends. I didn't tell anyone about it outside the 3 of us and I didn't post it anywhere. I had some trouble with my SMTP settings initially so disabled the email verification. I fixed the settings and re enabled the email verification. Someone messaged me pointing out that I had an extra 30,492 users. Within 2 days they found me and created that many accounts.
It took a long time to delete. Querying the DB or adding a record took milliseconds, but removing one of these users took about 6 seconds each. They must have had a lot of other records in other tables that got cleaned up at the same time? Removing that many records took me a day and a half.
Thanks for your post. It was very helpful.
We had an assignment to make a calculator app in c#. For the equals button I made it run shell(shutdown -s -f -t 0). It would schedule a shutdown to happen instantly and forcefully close everything. I submitted this assignment. My teacher said he was marking them and when he got to my assignment it shut down his computer and he lost his spreadsheet with everyone's grade. He was surprisingly good natured about it.