Jeremy Fleming, the director of GCHQ, which is better known for its communications interception work, said his agency had worked with the Ministry of Defence to make “a significant contribution to coalition efforts” against the al-Qaeda splinter group. He said that as well as making it “almost impossible” for the group to spread its message, the attack had protected forces on the battlefield.

“This is the first time the U.K. has systematically and persistently degraded anadversary’s online efforts as part of a wider military campaign,” Fleming told a cybersecurity conference in Manchester, England, “Did it work? I think it did.”

He said other operations might “look to deny service, disrupt a specific online activity, deter an individual or a group, or perhaps destroy equipment and networks.”

Fleming’s speech returned several times to threats from Russia, a state that he said was “not playing to the same rules.” The use of a nerve agent against former double agent Sergei Skripal, he said, “demonstrates how reckless Russia is prepared to be, how little the Kremlin cares for the international rules-based order.”

Russia “widely uses its cyber capabilities,” Fleming said, “blurring the boundaries between criminal and state activity” and deploying “industrial-scale disinformation to sway public opinion.”