SAP has moved the location of the Security Guides, so I thought I would post the location for SAP BPC 10 NW Security Guide:
http://help.sap.com/bopac#section3
You can easily get to all of the other versions from this same link, just by using the links on the left-hand side of the web page.
I hope this is helpful for you, as it took me a bit to find...
Jeff