Security Assist is not available as a stand alone product.
It is only available as part of the Data Bridge extension:
http://www.webassist.com/dreamweaver-extensions/data-bridge
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.