The FBI is investigating what’s being called a Russian cyber attack on the Democratic National Committee that resulted in a flood of internal emails being leaked to the public.

The investigation comes after DNC Chairwoman Debbie Wasserman Schultz abruptly resigned on Sunday after the leaked emails, posted on WikiLeaks, showed party officials conspiring to damage the campaign of Sen. Bernie Sanders, an Independent from Vermont.

“The FBI is investigating a cyber intrusion involving the DNC and [is] working to determine the nature and scope of the matter,” according to an email from a bureau spokesman.

The statement didn’t mention Russia, but The Washington Post reported last month that Russian spies had hacked the DNC and “so thoroughly compromised the DNC’s system that they also were able to read all email and chat traffic.”