According to unverifiable sources, an NSA contractor stored classified data and hacking tools on his home computer, which were made available to Russian hackers through the contractor's use of Kaspersky Lab anti-virus software [reuters.com]:
Russian government-backed hackers in 2015 stole U.S. secrets on how to penetrate foreign computer networks and protect against cyberattacks after a National Security Agency contractor put highly classified information on his home computer, The Wall Street Journal reported on Thursday, citing unidentified sources.
The contractor used a popular antivirus software by Russia-based Kaspersky Lab that may have made it possible for the hackers to identify and target the contractor's files, multiple sources told the Journal.
Experts consider the theft, which was not discovered until the spring of 2016, one of the most significant security breaches of recent years, the newspaper said, including details of how the NSA penetrates foreign computer networks, the computer code it uses for such spying and how it defends networks inside the United States, the sources told the Journal.
This may be the source of files released by The Shadow Brokers [wikipedia.org]. According to yet another anonymous source [nbcnews.com], the lax contractor in question is not Harold Martin [soylentnews.org].
Previously: NSA ‘Shadow Brokers’ Hack Shows SpyWar With Kremlin is Turning Hot [soylentnews.org]
The Shadow Brokers Identify Hundreds of Targets Allegedly Hacked by the NSA [soylentnews.org]
"Shadow Brokers" Release the Rest of Their NSA Hacking Tools [soylentnews.org]
Fearing Shadow Brokers Leak, NSA Reported Critical Flaw to Microsoft [soylentnews.org]
Kaspersky Lab has been Working With Russian Intelligence [soylentnews.org]
FBI Reportedly Advising Companies to Ditch Kaspersky Apps [soylentnews.org]
Federal Government, Concerned About Cyberespionage, Bans Use of Kaspersky Labs Products [soylentnews.org]