Nasdaq OMX boss Robert Greifeld said on Friday that his company’s systems work 99.99 per cent of the time. But when they do not, it is a huge deal. Last week’s outage raised concerns about growing market complexity – and whether Mr Greifeld should be sacked.

Nasdaq’s own investors are not too worried. When the market reopened, its?shares ended down just 3?per cent. This makes sense in as much as the direct financial impact of losing half of day of trading is minuscule. The real damage is reputational. This is not the exchange’s first big stumble. Bungling Facebook’s listing led to a regulatory fine and Nasdaq agreed to pay $62m to brokers; so far, no comparable hit is expected this time. Still, a humiliated Nasdaq could lose listings, which make up 13 per cent of operating profit.

All this comes at a time when competition may increase – BATS Global Markets and Direct Edge are in talks over a merger that would unseat Nasdaq as the second-largest US share-trading venue. Nasdaq’s latest problem also happened after glitches elsewhere in recent weeks, which should spur renewed efforts on reliability. That is needed, but would cost Nasdaq in human and financial resources.