Ques : What is NAT and ICS ?

  The security systems and methods are for securing operating system and data on physical hard disk. This security system is of no use if an attacker is able to sniff network packets.

Network Address Translation (NAT), is used to mask internal IP addresses with the IP address of the external Internet connection. Networks require NAT in their security policies to add an additional security "layer" between the Internet and the intranet. NAT function by taking a request from an internal client and making that request to the Internet on behalf of the internal client. In this configuration clients on the internal network, on local LAN, are not required to have a public IP address, thus conserving public IP addresses. The internal clients can be provided with an IP address from the private network blocks. Private IP addresses are not routed on the Internet and the address ranges are:

Private IP Addresses
10.0.0.0 - 10.255.255.255
172.16.0.0 - 192.168.255.255
192.168.0.0 - 192.168.255.255

However, Microsoft has designated a range for private addressing, 169.254.0.0 - 169.254.255.255.

NAT is an integral part of Routing and Remote Access Services (RRAS), as well as part of Internet Connection Sharing (ICS). The version of NAT used by ICS is scaled down form file full version, and does not allow for the level of configuration that the RRAS NAT allows. ICS is for a small office or for a home network, where there is one Internet connection that is to be shared by the entire network. All users connect via a single interface, usually connected via a modern, DSL, or cable access point.