Details of the breach, which happened back in 2015, are naturally hush-hush, but according to multiple sources familiar with the matter, this is how it went down. A contractor for the NSA brought highly classified material outside of NSA offices to his home computer. State-sponsored Russian hackers were then able to pilfer these files easily from the contractor’s relatively unprotected home network. These files contained information on how the NSA infiltrates computer networks of other countries, like Russia, and how it also defends its own networks from spying by other countries, like Russia. In other words, it leaves the NSA not only with less capabilities to hack into Russian networks but also less capable of protecting itself from future attacks.