New York (CNN) The Democratic National Committee claims that in the days after the 2018 midterm elections it was likely targeted by a group of Russian intelligence hackers, according to court documents filed overnight.

The hackers posed as a State Department official in the attempted hack, a senior Democratic Party source with direct knowledge of the attempt told CNN.

Dozens of DNC email addresses received spear-phishing emails that were ostensibly sent from a State Department official, the source said. The emails contained a PDF attachment that, if opened, was designed to gain access to systems through the recipient's computer, the source explained.

The DNC said it did not believe the attempt was successful.

In a court filing that is part of an an ongoing civil lawsuit against the Russian government, President Donald Trump, WikiLeaks and others, the DNC explained it believed the spear-phishing campaign was likely orchestrated by a Russian hacking group known as "Cozy Bear." The DNC said the timing and contents of the emails shared characteristics with a suspected Cozy Bear campaign that had been identified by the cybersecurity firm FireEye.

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