The Democratic National Committee has had its computer network breached and confidential files, including data on Donald Trump, stolen by Russian hackers, according to a report in the Washington Post.

Investigators say some of the hackers, who reportedly have links to the Russian Government, had access to the systems since last summer. During this time they were able to monitor all email and chat traffic.

The most recent attack saw the pilfering of an entire database of opposition research on Republican presidential candidate Donald Trump. It’s unclear precisely what information the trove contained, but it’s likely to have included details of his business dealings and previous political statements that the Democrats could use against him.

Crowdstrike, the cybersecurity firm hired by the DNC to investigate the intrusion, said two different Russian hacking groups working independently of each other infiltrated the network. The first, codenamed Cozy Bear, had been inside the system for almost a year and targetted DNC’s communications. The second, codenamed Fancy Bear, had breached DNC computers back in April and was looking for certain research, such as the Trump data.

Crowdstrike’s Chief Technology Officer, Dmitri Alperovitch, wrote in a blog post that the groups were most likely working for various branches of the Russian government, such as the federal security service (FBS) and Russian military intelligence.

“Everyone around the world is trying to figure out, ‘Who is Mr Trump?’” said Alperovitch. “What is his foreign policy going to be? What is it going to be in relation to Russia? He’s said some complimentary things about Putin. How real is that?”

No donor or personal information was compromised, according to the report, which stated that the hackers also targetted the personal websites of both Trump and Hilary Clinton, though it’s not clear if those attacks were successful.