WASHINGTON - Suspected terrorists have changed how they communicate and have become more difficult to track as a result of former contractor Edward Snowden's disclosures about U.S. surveillance operations, according to current and former officials, who say that the changes have led to a significant loss of intelligence.
How much that loss amounts to remains unknown as the government's classified assessment is continuing, they said.
In addition, Snowden's disclosures about eavesdropping in Russia and China gave each of those countries insights that are already thought to have impaired the National Security Agency's ability to intercept their communications, the officials said.
Among the disclosures from Snowden that were published in the Washington Post and the Guardian was that Skype, the Internet calling service, was among the systems that provided data to the NSA's secret PRISM database. That disclosure contradicted a widespread belief that calls made via Skype were difficult or impossible to intercept.
Some alleged terrorists the NSA was tracking are no longer using Skype, U.S. officials say. Others have stopped using e-mail, said one U.S. official who has been briefed on the damage.
"The Skype thing was really bad," the official said.
The inability to use such common communications systems creates problems for terrorist groups by reducing their ability to share plans and coordinate, but it also costs intelligence agencies information, the official said.
Osama bin Laden had been savvy enough to take extreme measures to avoid emitting an electronic signature: his compound in Abbottabad, Pakistan, had no Internet or phone service, and his couriers took the batteries out of their cellphones when they approached within miles of the location.
Most rank-and-file militants either can't afford to be that careful or have simply not tried to, the official said. The disclosures about the NSA's ability to track phone calls and e-mail are changing that to some extent, the official said.
On the foreign intelligence side, government officials are continuing to try to determine how much specific information Snowden knew about the methods the U.S. uses to eavesdrop on other countries. Former counterintelligence officials say they believe there has already been serious damage, and fear it could worsen, depending on what Snowden had.
Counterintelligence officials say they believe that whatever information Snowden has with him probably has fallen into the hands of Chinese or Russian intelligence or both by now.
According to the Guardian, Snowden gave the newspaper a document showing that the NSA had intercepted the communications of then-Russian President Dmitry Medvedev during his visit to Britain for a Group of 20 summit in London in 2009.
Snowden also disclosed in an interview with the South China Morning Post the specific dates and the IP addresses of computers in Hong Kong and on the Chinese mainland hacked by the NSA over a four-year period, the paper said.
"He's told them implicitly a great deal about our capabilities that they didn't know," said Joel Brenner, a former senior NSA lawyer who also was the nation's top counterintelligence official from 2006 to 2009. "This kind of disclosure has serious consequences."
