The breach happened after a software error at the technology company NGP VAN, which provides campaigns with voter data. As a result of the glitch, “all users on the system across the Democratic campaigns were inadvertently able to access some data belonging to other campaigns for a brief window,” DNC spokesman Luis Miranda said in a statement.
The Clinton campaign declined to comment.
Sanders’ campaign said it had fired a staff member who accessed the Clinton campaign’s data. A DNC official said that it is believed a total of four people breached Clinton’s data.
In a statement, Sanders’ campaign faulted NGP VAN, the data systems vendor, for continuing to “make serious errors.”
“On more than one occasion, the vendor has dropped the firewall between the data of different Democratic campaigns,” the campaign said. “Our campaign months ago alerted the DNC to the fact that campaign data was being made available to other campaigns. At that time our campaign did not run to the media, relying instead on assurances from the vendor.
“Unfortunately, yesterday, the vendor once again dropped the firewall between the campaigns for some data.”
The Washington Post was the first media outlet to report the breach.
Sanders and Clinton will meet next at the Democratic debate on Saturday.