"The leaks from Snowden have been very damaging, they put our operations at risk. Our adversaries are rubbing their hands with glee. Al-Qaeda is lapping it up," John Sawers told lawmakers.
The head of Britain's electronic listening service GCHQ, Iain Lobban, told the same parliamentary committee that the Snowden revelations had led "terrorist groups" in the Middle East, Afghanistan and elsewhere to alter the way they communicate.
"We have intelligence on (and) we have actually seen chat around specific terrorist groups, including closer to home, discussing how to avoid what they now perceive to be vulnerable communications methods," Lobban said.