Network Address Translation (NAT) was first codified as RFC1631 in 1994. NATs primary objective was to make 32-bit IP numbers go further, in order to buy us time to update to IPv6. Used responsibly, NAT can increase your resilience to external attack. But it is a snake-oil substitute for a proper network security regimen, not to make it more secure. Even if NAT helps to stop a virus like Conficker from sneaking into your LAN, it wont stop the virus from wandering around inside your LAN if it gets in via other means.”]
Source: https://nakedsecurity.sophos.com/2009/11/18/security-byaccident/