Walter Russell Mead points to a Financial Times report detailing how, as soon as the U.S. started raining bombs on the Islamic State, the group’s fighters started curtailing their Internet activities. They even appear to be doing so in ways especially designed to avoid detection by certain Western signals-intelligence methods:

When bombs rained down before the internet age, targets pulled curtains shut and dimmed their lights. But for the jihadis of the Islamic State of Iraq and the Levant, ISIS, more modern countermeasures apply: stopping tweets and scrubbing metadata. . . .
An Arabic language manual distributed among ISIS fighters, a copy of which was seen by the Financial Times, gives detailed instructions on how to remove metadata from content being put online.
“A number of security gaps have appeared that have benefited the enemy and have helped expose the identities of some brothers or identify some sites used by the mujahideen with ease,” it begins, going on to explain in detail what those gaps are and the way they expose “data that could turn your hair gray”.

Similar observation tactics, the report says, were used against al-Qaeda in Iraq in the 2000s (the Islamic State’s predecessor), but the group’s new iteration seems to be more savvy. “The report,” Mead says, “lends credence to an argument made by Snowden’s critics—that his disclosures would carry a high cost for the United States and its allies during actual wartime operations.” It’s unclear just how closely the Islamic State’s protocols are tied to what was in the documents Snowden disclosed, but there’s no doubt Snowden’s operation caused terrorists worldwide to be vastly more careful about their online and cellular communications — being more careful about more rapidly replacing phones, etc. And that’s before one even gets into the specific counterterrorism, drug-interdiction, and other operations, many of which haven’t been explained in broad detail, across the globe that Snowden’s reports exposed to a great enough extent that they had to be shut down.