Accidental on purpose?
I was visiting a customer and was peripherally involved in a problem they had.
They had a home grown configuration file which had had change upon changed made to it - to the extent that no one knew how it worked. They had had meetings to discuss rewriting it, and thought the risk was too high of it not working.
I was at the customer for the weekend while they did a major upgrade, and they wanted all support people in. One person I was working with thought he could improve their configuration program.
At midnight, he found his changes made it worse; and then he found he was updating the master copy, and when he backed out his changes it didn't work. The previous backups were corrupted, so could not be used.
He bit the bullet and rewrote it from scratch.
I went to the hotel at 0600, and came back at 1500 for the next day's support. He was still there. In the middle of the night I found him asleep at his desk (for an hour or two).
Sunday night about 8pm the major upgrade was successful, and the rewrite worked.
The guy was hyperactive from coffee an doughnuts. He said that most of the work was understanding what was still needed, and what was junk left over from earlier systems.
His boss when told, was happy and annoyed (more happy than annoyed).
As I was checking some documentation on his laptop, I noticed some files saying backup of....
When I mentioned it, he said "you didn't see them I sort of caused the backups to be unreadable. I just wanted to fix this application"