This morning’s Observer column.

On Tuesday 23 April, a tweet from Associated Press (AP) revealed startling news. There had been explosions in the White House and Obama had been injured. The tweet was a hoax – the AP Twitter account had been hacked via a clever phishing exploit – but it briefly caused havoc. The Dow Jones Industrial Average dropped 144 points between 10.07am and 10.09am, for example. Crude oil prices also briefly tumbled and the price of US Treasury bonds and gold futures spiked. Within minutes, AP disclosed that the tweet was erroneous and things returned to normal, with the Dow eventually rising 152 points for the day to close at 14,719.

Crisis over, then? Er, not quite. The story of the hoax AP tweet resurrects troubling thoughts about systems and fragility…