by Ken Task.
"Let's say ..." ... actually because there are some areas of moodle config (like users) that have utilities via command line, Moodle might actually be more secure than mentioned CMS's (I've used/am using both CMS's, BTW).
That being said, query your mdl_user table for auth=manual - accounts that will auth using mdl_user table.
mysql> select id,firstname,lastname,username from mdl_user where auth='manual';
The guest account, using or not using is ID 1 and set to manual and probably should remain. User ID 2 was/is the first person to install ... default for login name was 'admin'. ID 2 is probably the one you want to change.
There is a command line only script in code/admin/cli/ that can reset manual accounts (need ssh access to server).
cd /path/to/moodlecode/admin/cli/
php reset_password.php [ENTER]
You will be pompted for the user name first.
Then the new password ... in clear text but no worries there ... you are in an ssh shell.
One can also set an account to be admin via config.php by adding a line:
$CFG->siteadmins='2,#,#';
where #,# are user ID numbers from mdl_user table.
Using config.php file should be last resort ... just to get in an set users desired to admin levels. Once you have admin users squared away, comment out the CFG line in config.php and it's no longer in affect. Comment out by adding // in front of the line.
Might leave the line in config.php just in case you need such 'back doors' in near future.
'Spirit of Sharing', Ken