On Monday, a hacking group calling itself the “ShadowBrokers” announced an auction for what it claimed were “cyber weapons” made by the NSA. Based on never-before-published documents provided by the whistleblower Edward Snowden, The Intercept can confirm that the arsenal contains authentic NSA software, part of a powerful constellation of tools used to covertly infect computers worldwide.

The provenance of the code has been a matter of heated debate this week among cybersecurity experts, and while it remains unclear how the software leaked, one thing is now beyond speculation: The malware is covered with the NSA’s virtual fingerprints and clearly originates from the agency.

The evidence that ties the ShadowBrokers dump to the NSA comes in an agency manual for implanting malware, classified top secret, provided by Snowden, and not previously available to the public. The draft manual instructs NSA operators to track their use of one malware program using a specific 16-character string, “ace02468bdf13579.” That exact same string appears throughout the ShadowBrokers leak in code associated with the same program, SECONDDATE.

SECONDDATE plays a specialized role inside a complex global system built by the U.S. government to infect and monitor what one document estimated to be millions of computers around the world. Its release by ShadowBrokers, alongside dozens of other malicious tools, marks the first time any full copies of the NSA’s offensive software have been available to the public, providing a glimpse at how an elaborate system outlined in the Snowden documents looks when deployed in the real world, as well as concrete evidence that NSA hackers don’t always have the last word when it comes to computer exploitation.

But malicious software of this sophistication doesn’t just pose a threat to foreign governments, Johns Hopkins University cryptographer Matthew Green told The Intercept:

The danger of these exploits is that they can be used to target anyone who is using a vulnerable router. This is the equivalent of leaving lockpicking tools lying around a high school cafeteria. It’s worse, in fact, because many of these exploits are not available through any other means, so they’re just now coming to the attention of the firewall and router manufacturers that need to fix them, as well as the customers that are vulnerable. So the risk is twofold: first, that the person or persons who stole this information might have used them against us. If this is indeed Russia, then one assumes that they probably have their own exploits, but there’s no need to give them any more. And now that the exploits have been released, we run the risk that ordinary criminals will use them against corporate targets.

The NSA did not respond to questions concerning ShadowBrokers, the Snowden documents, or its malware.

A Memorable SECONDDATE

The offensive tools released by ShadowBrokers are organized under a litany of code names such as POLARSNEEZE and ELIGIBLE BOMBSHELL, and their exact purpose is still being assessed. But we do know more about one of the weapons: SECONDDATE.

SECONDDATE is a tool designed to intercept web requests and redirect browsers on target computers to an NSA web server. That server, in turn, is designed to infect them with malware. SECONDDATE’s existence was first reported by The Intercept in 2014, as part of a look at a global computer exploitation effort code-named TURBINE. The malware server, known as FOXACID, has also been described in previously released Snowden documents.

Other documents released by The Intercept today not only tie SECONDDATE to the ShadowBrokers leak but also provide new detail on how it fits into the NSA’s broader surveillance and infection network. They also show how SECONDDATE has been used, including to spy on Pakistan and a computer system in Lebanon.

The top-secret manual that authenticates the SECONDDATE found in the wild as the same one used within the NSA is a 31-page document titled “FOXACID SOP for Operational Management” and marked as a draft. It dates to no earlier than 2010. A section within the manual describes administrative tools for tracking how victims are funneled into FOXACID, including a set of tags used to catalogue servers. When such a tag is created in relation to a SECONDDATE-related infection, the document says, a certain distinctive identifier must be used: