Western nations should brace for more cyber security attacks on critical infrastructure from "second tier" nation states, as warfare from developing nations increasingly shifts online, according to a US cyber security expert who spent more than 30 years with the National Security Agency.

Phil Quade, who has recently become chief information security officer at cyber security software firm Fortinet, rose through the ranks of the NSA in his three-decade long career, serving in both "offensive" and "defensive" capacities, protecting the country's secrets and attacking adversaries.