As online threats race up national security agendas and governments look at ways of protecting their national infrastructures a cyber arms race is causing concern to the developed world.
Benjamin Lawsky, head of the New York Department of Financial Services, admitted this summer that he was concerned about the vulnerability of the US financial system when he raised the prospect of an "Armageddon-type cyber event".
Before a joint conference on cyber security in Manhattan on Wednesday with Cyrus Vance, the New York district attorney, Mr Leppard expressed similar fears for Britain.
"We look at terrorism and you think . . . if global trading stopped that would have an enormous impact on western society, global society . . . at the heart of capitalism," the commissioner told the Financial Times.
"There could be a very serious impact to the financial institutions of the world through a cyber attack and I think it's a very strong likelihood that it will happen one day in the future, which is why we've got to push back and take action now before it happens," Mr Leppard said.
Singling out Islamic State of Iraq and the Levant, known as Isis, as a potential perpetrator, the commissioner said western society needed to find a way to balance the benefits of technological progress with the "huge harm" it could wreak on financial markets.
"There'll be evidence to suggest that all of the stock exchanges in the world have been breached in the last 10 years, Nasdaq, London Stock Exchange, all of them," he said.