The primary purpose of Network Access Protection (NAP) is to prevent:

The primary purpose of Network Access Protection (NAP) is to prevent:
A . Loss of data from client computers on a network.
B . Non-compliant systems from connecting to a network.
C . Users on a network from installing software.
D . Unauthorized users from accessing a network.

Answer: B

Explanation:

NAP enforces health policies by inspecting and assessing the health of client computers, restricting network access when client computers are noncompliant with health policy, and remediating noncompliant client computers to bring them into compliance with health policy before they are granted full network access. NAP enforces health policies on client computers that are attempting to connect to a network; NAP also provides ongoing health compliance enforcement while a client computer is connected to a network.

Reference: http://technet.microsoft.com/en-us/library/cc754378(v=ws.10).aspx