Last night, browsing the lists of members, I realized that a new registered member, was already a director!
That is very weird. There is no known security issue in xenforo that will allow that. Have you installed any mods lately or made some other kind of modification to your forum?I looked in the log no one has put this user administrator.How strange, I hope this is not a security bug
What he probably means is that someone registered with the username "administrator".
If its PayPal related to purchasing an upgrade, I would check your settings for any paid upgrades you've defined. But as Brogan said above, you can only add administrators / moderators through the ACP and they won't have complete access to your site except as defined in Usergroup Permissions.