WASHINGTON — Suspected terrorists have changed how they communicate and have become more difficult to track as a result of former NSA contractor Edward Snowden’s disclosures about U.S. surveillance operations, according to current and former officials.
They said the changes have led to a significant loss of intelligence.
The extent of that loss 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 already are 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 suspected terrorists the NSA was tracking are no longer using Skype, U.S. officials said. Others have stopped using email, said one U.S. official who has been briefed on the damage.
“The Skype thing was really bad,” the official said.
Skype developed its reputation for security for several reasons. The service routes calls between computers through the Internet rather than telephone networks, which avoids traditional wiretaps. And the system uses encryption technology for the contents of its calls and text messages.
But the encryption has limits. For example, Microsoft, which owns the service, is able to scan the contents of communications to search for spam and other forms of computer malware. The company also stores records of communications to comply with legal requirements.
The inability to use 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.