Today we wanted to upgrade our production site from Moodle 2.2 to 2.4. However during the process it turned out that students were able to access the site (still in maintenance mode) and some of them ran the upgrade... On our site students are enrolled through LDAP.

Here is what happened:
1. Moodle was put into maintenance mode
2. Backups were done
3. Updated files were pulled in approx 20 mins later
4. Basically the instant the files were up, people were running the upgrade

Please let me know if you need more details.

This issue is duplicated in CONTRIB-4256 - I am sorry for the duplicate, but I did not notice that the project field defaulted to Add-ons...