ISA Server, like any product, will have updates and patches made available as the product matures. To ensure the security of your product, you should test and then apply these patches as they become available. Follow these general steps to apply updates:
Check the Microsoft ISA Server Download site at http://www.microsoft.com/isaserver/downloads/2004.asp.
Download the patches and read the documentation that is made available with the download.
Before you patch the server, ensure that you follow the appropriate process to inform users, or provide alternative access to required networks.
If the patch will stop firewall functionality, physically disconnect the ISA server from untrusted networks.
Apply the patch according to the instructions.