When users connect over the Internet, a whole new set of security issues is introduced. If you already have external connection security policies in place, chances are good that they will apply to SharePoint Server 2007 and cover a user's connection to the portal site. Port 80 is the most often attacked port, and even with the use of Secure Sockets Layer (SSL), external connections offer an obvious attack vector to a would-be hacker. Creating policies that detail acceptable behavior for your users when they connect to the portal site will help ensure that their connection is done securely.
If you do not already have such policies in place, consider the following:
All Internet Web servers must be firewall protected.
SharePoint Server 2007 servers must be in the perimeter network.
Internet portal servers must be placed on a separate subnet.
Connection to intranet portal servers from the Internet requires encryption and certificates.
Employee-owned computers must meet minimum software requirements.
Vendor connectivity to intranet from the Internet is prohibited.
Customer connectivity to customer sites from the Internet requires encryption and certificates.