When the Syrian Electronic Army managed to hack the Twitter account of the Associated Press and sneak out a false report of explosions at the White House to the news agency’s 1.9m followers it scored its biggest coup to date.

The report caused a brief but sharp dip in the US stock market. It also illustrated how the Syrian hackers, who target entities opposed to the regime of President Bashar al-Assad, could use relatively simple techniques to turn their gadfly disruptions into something more menacing.

“When you start to do things that have a big impact on the stock market, you are getting away from hacking and moving much closer to something that resembles an actual cyber attack on the US – which takes things into a different area altogether,” said one former US official involved in cyber security.