Authorize.net seal and JS in footer
Where are you trying to add the script -- in the "Footer" editor window on the Event details page? 

If so, you probably need to add it in the Wordpress side (e.g. as an HTML/Text widget) rather than the CiviCRM editor to avoid these security notices. If you only want to have the widget show on CiviCRM pages, or SSL pages, etc. you may find this Q&amp;A on the Wordpress StackExchange site helpful (more than one of the answers may be useful).