If you're an Authorize.Net user running a StoreFront 2000 web site, then this is a "must have" upgrade. It provides a greatly improved level of security & reliability over the obsolete built-in Authorize.Net methods. This add-on also supports using one Authorize.Net account for multiple SF2000 stores!
From the Authorize.Net site:
AuthNetSSLConnect is a COM control object. It contains a COM object named SSLPost that uses Authorize.Net's Direct Response interface to submit a transaction to Authorize.Net without using a browser. This allows any Windows-based program or script to submit transactions and receive direct responses from the server.
Requires the AuthNetSSLConnect component be installed on your secure server (testing script included). Installation (1 hour) is available.