American cyber security behemoth Symantec suffered a breach of its systems in February but kept quiet about it even though passwords and a list of companies said to be its clients were stolen by an attacker.

There are many things that one can say about America's premier spy agency, the NSA, but one can never accuse it of not instilling an incredible degree of loyalty among most of its employees, to the extent that those who left its portals decades ago still carry water for it when someone attacks the agency.

Symantec president and chief executive Greg Clark has suddenly left his post before a permanent replacement was in place, with the company naming director Richard Hill as a temporary fill-in. Clark was the fifth top executive to quit in the last six months.