A spokesman for Bernie Sanders’ presidential campaign confirmed late Thursday that it had fired a staffer responsible for accessing confidential information from Democratic rival Hillary Clinton's campaign.

Following the data breach, which happened Wednesday, the Democratic National Committee (DNC) suspended Sanders’ access to the party’s master voter file — cutting off his campaign’s access to a goldmine of information about voters across the nation. 

“After discussion with the DNC it became clear that one of our staffers accessed some modeling data from another campaign,” Sanders’ communications director Michael Briggs reportedly said. “That behavior is unacceptable and that staffer was immediately fired.”

Bloomberg, citing two people familiar with the matter, identified the fired staffer as the campaign’s national data director Josh Uretsky. Sanders' campaign has so far not named the employee but Briggs blamed NGP VAN — the company that administers the DNC’s voter file — for the breach, which was first reported by the Washington Post Thursday.

“On more than one occasion, the vendor has dropped the firewall between the data of different Democratic campaigns. Our campaign months ago alerted the DNC to the fact that campaign data was being made available to other campaigns,” Briggs reportedly said. “Sadly, the vendor who runs the DNC's voter file program continues to make serious errors.”

Meanwhile, the DNC, which said that the Sanders campaign's access to the database would remain suspended until it provides proof that all accessed data have been deleted, reportedly asked the firm to conduct an analysis to identify users who accessed other campaigns’ data, and to conduct a full audit of its system.

“The DNC places a high priority on maintaining the security of our system and protecting the data on it,” the DNC’s communications director Luis Miranda reportedly said. “We are working with our campaigns and the vendor to have full clarity on the extent of the breach, and to ensure that this isolated incident does not happen again.”

The DNC's move, which came ahead of Saturday’s Democratic debate and less than two months from the first caucuses and primaries, could prove to be a significant setback for Sanders, who is already lagging behind Clinton in opinion polls.