The site technical contact should subscribe to the Drupal security notifications list. You can receive notifications via email, RSS, and/or Twitter.
To receive email notifications: Create an account on drupal.org
or log in to your existing account On your account page, click Edit, then click My Newsletters. Check the box labeled Security announcements and save your settings.
Security announcements for Drupal core and contributed modules and themes are sent weekly, or as necessary for highly critical updates.