New in Windows Vista, the Network Access Protection Agent service is used for controlling network access of a computer based on its ‘health’. The ‘health’ of the system is determined by a policy defined by the network administrator which might measure parameters like anti-virus signature level, firewall status, or OS patch levels in an effort to determine if the computer is ‘fit’ enough to be a peer on the network. This is only needed for Enterprise installations and requires Windows Server 2008 to do the ‘health check’, but since it is set to Manual by default, there is no benefit to disabling it.