In 2012, the director general of MI5 revealed that a London-listed company had lost £800 million as a result of a state-backed cyber attack. The company in question has not been publicly identified and no disclosures were made to the market. Why was the market not notified?

That question is one that is likely to gain in importance. In a sign of how seriously the authorities are taking the threat, the Bank of England last month published a report on an exercise carried out last year to test the response of the banking sector and the financial markets to a simulated cyber attack by a hostile foreign state.