On Monday, the Intercept published a classified internal NSA document noting that Russian military intelligence mounted an operation to hack at least one US voting software supplier—which provided software related to voter registration files—in the months prior to last year's presidential contest. It has previously been reported that Russia attempted to hack into voter registration systems, but this NSA document provides details of how one such operation occurred.

According to the Intercept:

The top-secret National Security Agency document, which was provided anonymously to The Intercept and independently authenticated, analyzes intelligence very recently acquired by the agency about a months-long Russian intelligence cyber effort against elements of the US election and voting infrastructure. The report, dated May 5, 2017, is the most detailed US government account of Russian interference in the election that has yet come to light.

While the document provides a rare window into the NSA's understanding of the mechanics of Russian hacking, it does not show the underlying "raw" intelligence on which the analysis is based. A US intelligence officer who declined to be identified cautioned against drawing too big a conclusion from the document because a single analysis is not necessarily definitive.

The report indicates that Russian hacking may have penetrated further into US voting systems than was previously understood. It states unequivocally in its summary statement that it was Russian military intelligence, specifically the Russian General Staff Main Intelligence Directorate, or GRU, that conducted the cyber attacks described in the document:

Russian General Staff Main Intelligence Directorate actors … executed cyber espionage operations against a named U.S. company in August 2016, evidently to obtain information on elections-related software and hardware solutions. … The actors likely used data obtained from that operation to … launch a voter registration-themed spear-phishing campaign targeting U.S. local government organizations.

Go read the whole thing.