FBI Confirms Investigation Into Massive Hack of DNC

"A compromise of this nature is something we take very seriously," FBI says.

"The FBI is investigating a cyber intrusion involving the DNC and are working to determine the nature and scope of the matter," the FBI said in a statement today. "A compromise of this nature is something we take very seriously, and the FBI will continue to investigate and hold accountable those who pose a threat in cyberspace."

For weeks, the FBI had been unwilling to confirm it was looking into the hack — or even that such a hack had taken place, as The Washington Post first reported in June.

Nevertheless, a cybersecurity firm working with the DNC spoke extensively at the time about how the DNC was hacked by "two separate Russian intelligence agencies."

The hackers were "looking for opposition research on Trump and his campaign" and "they did take opposition research on Trump," Alperovitch said at the time.

"This also shows you espionage has now moved off the just physical realm of recruiting spies and getting information. It's now through cyber means. This is a traditional target of Russian intelligence for 100 years but now doing it for cyber," he said, referring to U.S. candidates and campaigns. "I would say this is not surprising at all. This is what intelligence agencies" want to get.

He said that the DNC is "absolutely" safer now and that CrowdStrike did a full remediation and "kicked out both adversaries." He added that CrowdStrike installed software because the firm "expect[s] for them to come back."

"Russian intelligence's interest in the U.S. political system will not cease. It will only intensify, and there will be ongoing attempts to hack into the network going forward," Alperovitch said.

ABC News' Alana Abramson contributed to this report