https://www.theverge.com/2017/10/5/16431564/kaspersky-russian-hackers-nsa-document-breach

In 2015, Russian agents stole highly classified NSA materials from a contractor, according to a new report in The Wall Street Journal. It’s a major breach of internal security, made possible after the contractor transferred the materials to his home computer in violation of known security procedures.

Even more alarming is how the foreign agents became aware of that violation. According to the report, the hackers seem to have identified the files — which contained “details of how the U.S. penetrates foreign computer networks and defends against cyberattacks” — after an antivirus scan by Kaspersky antivirus software, which somehow alerted hackers to the sensitive files.