Biden admin vows to hold Chinese hackers responsible after government email breach

National security adviser Jake Sullivan says investigators are still looking into the hack of a Microsoft system that gave access to U.S. government emails.

"This was actually an intrusion into a Microsoft cloud system, and through that cloud system they got into unclassified U.S. government emails. It was the U.S. government who discovered the intrusion, alerted Microsoft, got it shut down. And now we're taking steps to ensure that's not an ongoing vulnerability," Sullivan said. Anders Hagstrom is a reporter with Fox News Digital covering national politics and major breaking news events. Send tips to Anders.Hagstrom@Fox.com, or on Twitter: @Hagstrom_Anders.

"Secondly, this is the type of activity and behavior that we have seen from multiple foreign adversaries over multiple administrations. And in every case, we take the necessary time and rigor to be able to fully investigate what happened, who did it, and what the best response is. We're still in the middle of that. So I'm going to leave it to our continued working through of this challenge. But as we have in the past, we will take steps to hold those who perform this responsible," he added.