Authentication: Unique Login
The goal of this authentication plug-in is to make sure that each user in Moodle only has one active session simultaneously.
To work properly, the plugin needs that Database-stored sessions are enabled. Have a look at the module documentation on http://docs.moodle.org/20/en/Uniquelogin_authentication to more information.
This plugin is being maintained by ED-ROM, the portuguese Moodle Partner.