Extremists are sharing media reports about the National Security Agency's telecommunications surveillance program and are urging each other to increase their security.
"Jihadi groups over the coming weeks will be going through a rapid evolution of their security measures in response to details revealed" in leaked NSA documents, said Ben Venzke, CEO of IntelCenter, which monitors open-source extremist communications for government clients.
Classified documents posted online last week revealed that the NSA can intercept emails, instant messages and Internet phone or video calls from nine service providers, using a system called Prism.
"If you are a bad actor and I tell you all email from company X is being monitored, are you going to continue to use company X or are you going to switch to company C that is not on the list?" said Mr. Venzke, who has followed jihadi messaging for more than a decade.
Among the measures being suggested is stopping the use of email and communications services listed in the leaked documents — Google, Microsoft, Yahoo, Facebook, Skype, YouTube, Paltalk, Apple and AOL.
Extremists on bulletin boards also are recommending "increased use of encryption tools," Mr. Venzke said.
Online jihadists have long urged their comrades to use encryption, which can shield an electronic communication from surveillance by scrambling the data of which it is composed. There is even an Arabic language computer encryption program called Mujahideen Secrets that members of one Web forum have been urged to use for several years.
Documents posted online last week revealed that the NSA has been collecting "metadata" — the time and length of telephone calls, the calling and receiving numbers, and the two parties' location — of about every call made or received in the United States.
In addition, the agency has been collecting massive amounts of content data — the texts of emails or the sounds of people talking on Internet calls — directly from Internet providers, although officials say this capability is used only against people "reasonably believed" to be foreigners outside of the United States.
Glenn Greenwald, the reporter for Britain's Guardian newspaper who broke the Prism story, has said the revelation will not hurt counterterrorism efforts because terrorists already know their communications are being monitored.
"There's not a single revelation that we've provided to the world that even remotely jeopardizes national security," he told NBC Monday.
But Mr. Venzke said: "Terrorists, hostile intelligence agencies, child pornographers and the rest of the world of nefarious actors for the most part can all read."
He said that terrorists and other intelligence targets may have "had a vague notion that this [surveillance] was going on" but likely were focused on other aspects of their plots, not communication security.
"I guarantee you it just went right to the top of their priority list," he said.
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