Hackers linked to the Russian government breached the Democratic National Committee’s servers and email system last summer, according to a new report in The Washington Post. A CrowdStrike investigation identified two separate groups, both linked to Russia, one of which maintained access until as recently as this April. The investigation linked one of the groups to the similar attack on the official State Department email servers last year.

Despite widespread system access, the attackers did not retrieve any financial or personal donor information from the DNC, leading investigators to believe the attack was motivated by espionage rather than fraud or data theft. The Russian government has officially denied involvement.

The attackers did retrieve significant information from the party’s opposition research file on presumptive Republican presidential nominee Donald Trump, which contains information to be used against him over the course of the campaign. Such files are a common political practice, but their contents are seen as extremely sensitive for both political and privacy reasons. It’s unclear what information the DNC had acquired on Trump, but the nature of the file makes it a natural target for a foreign power investigating possible political leaders abroad.

The Clinton and Trump campaigns were also targeted by the attackers, although it's unclear whether those efforts were successful.

Update 2:39 PM ET: Updated with denial from Russian government.