In 2013, hundreds of CIA officers — many working nonstop for weeks — scrambled to contain a disaster of global proportions: a compromise of the agency’s internet-based covert communications system used to interact with its informants in dark corners around the world. Teams of CIA experts worked feverishly to take down and reconfigure the websites secretly used for these communications; others managed operations to quickly spirit assets to safety and oversaw other forms of triage.

“When this was going on, it was all that mattered,” said one former intelligence community official. The situation was “catastrophic,” said another former senior intelligence official.

From around 2009 to 2013, the U.S. intelligence community experienced crippling intelligence failures related to the secret internet-based communications system, a key means for remote messaging between CIA officers and their sources on the ground worldwide. The previously unreported global problem originated in Iran and spiderwebbed to other countries, and was left unrepaired — despite warnings about what was happening — until more than two dozen sources died in China in 2011 and 2012 as a result, according to 11 former intelligence and national security officials.