The Islamist militants who have seized almost a third of Iraq and Syria pose the next great cyber threat as terrorist organisations hoard cyber weaponry from underground markets, the chief executive of FireEye has warned.

David DeWalt, who heads the leading new-generation cyber security company, said the Islamic State of Iraq and the Levant (Isis), would follow in the footsteps of the Syrian Electronic Army and the Iran-based Ajax Security Team to target western countries and companies with cyber attacks.

“We’ve begun to see signs that rebel terrorist organisations are attempting to gain access in cyber weaponry,” he said. “Isis has already had success in utilising technology, using the web for recruiting, distribution of terrorist information and scare tactics.”