Chinese hackers who breached Microsoft’s (MSFT.O) email platform this year managed to steal tens of thousands of emails from U.S. State Department accounts, a Senate staffer told Reuters on Wednesday.

The staffer, who attended a briefing by State Department IT officials, said the officials told lawmakers that 60,000 emails were stolen from 10 State Department accounts. Nine of those victims were working on East Asia and the Pacific and one worked on Europe, according to the briefing details shared via email by the staffer, who declined to be named.