Using Moodle 1.6.3+, Server 2003 on our production server a student somehow managed to get to the new user form. In trying to duplicate what the student had done I tried to login using wildcards for usernames and passwords.
The nightly backup worked well but received an error whilst doing a restore with a view to upgrading Moodle and the restore stopped and reported an error. The long and short of it was that whilst trying to insert the wildcards MYSQL 5.0.41 reported an error (1034) from mdl_log.
Deleting all the login errors from mdl_log WHERE action = error and doing another backup cured the problem.
I still don't know how the student got to new user page.