When Does CiviCRM Create a Contact Record for a User? When is a User Linked to an Existing Contact?
Whenever a new user registers, CiviCRM checks for an existing contact with the same email address.
Whenever an existing user logs in, CiviCRM checks for a linked contact record. If none exists, the same logic applies - either link the user to an existing contact or create a new contact. This case applies when CiviCRM is installed or enabled for an existing Drupal site. However, we recommend that you run the batch synchronization utility (next section) in this situation.
CiviCRM does not natively use the hooks and APIs of Joomla to facilitate hooking into the user registration and login pages. As a result, in com_user neither a new user registration nor an existing user login alone will trigger the above check for a corresponding CiviCRM contact. Instead, this check is made whenever a logged in Joomla user engages in a transaction with the CiviCRM system, such as editing a CiviCRM Profile form, making a Contribution or registering a Membership. You can, however, replace the Joomla registration form with a form that using a CiviCRM profile that has registration enabled.
However, you can create a user plugin that responds to one or more of the user events. In Joomla 1.5 those are:
In 1.6 those are