Authorize.net will be rolling out an integration with Akamai in the not too distant future.  They had it scheduled for 6/30/16, but have delayed it because vendors don't all appear to be getting ready as fast as Authorize.net hoped they would.

Three files will need to be changed in your Zen Cart to facilitate a smooth transition.

includes/modules/payment/authorizenet.php
includes/modules/payment/authorizenet_aim.php
includes/modules/payment/authorizenet_echeck.php