In the latest NSA data breach, the Wall Street Journal reports that hackers linked with the Russian government stole tools and files that reveal how the US slips into foreign computer networks and protects against cyberattacks. “The breach, considered the most serious in years, could enable Russia to evade NSA surveillance and more easily infiltrate U.S. networks.”

Hackers accessed the critical information after a contractor working for the NSA moved highly classified material to his home computer–a security violation in itself–and then ran antivirus software from Kaspersky.

As April Glaser writes in Slate, while Russia is reportedly culpable for this latest NSA hack, “the fact that the nation’s top surveillance agency seems to have such poor security itself is extremely unsettling.”

Read the full story in Slate.