(Reuters) — A top data staffer for Democratic presidential candidate Bernie Sanders has been fired amid allegations that the campaign breached voter data from rival Hillary Clinton’s campaign, media reports said on Friday.

The breach occurred for a brief period on Wednesday when staff at Sanders’ campaign were able to view confidential information from the Democratic National Committee, according to the Washington Post and NBC.

Sanders’ campaign acknowledged the breach in a statement and blamed it on the Democratic Party’s software vendor and said it was an isolated incident, the reports said.

Representatives for Sanders, Clinton and the DNC could not be immediately reached for comment.

A person familiar with the matter told CNN the staffer who was fired for accessing the voter data was Josh Uretsky, the campaign’s national data director. Uretsky told CNN he was not trying to take data from Clinton’s operation.

“We knew there was a security breach in the data and we were just trying to understand it and what was happening,” Uretsky told CNN on Friday, adding that he was trying to understand his candidate’s own campaign data vulnerability.

DNC communications director Luis Miranda said in a statement to CBS News that the vendor, NGP VAN, had been directed to analyze the breach and determine who accessed the data.

The Sanders campaign said in a statement, according to the reports, that the DNC is “relying on a incompetent vendor who on more than one occasion has dropped the firewall between the various Democratic candidates’ data.”

The Washington Post, which first reported the data breach late on Thursday citing several party officials, said discovery of the breach ignited alarm at the DNC.

News of the breach comes ahead of the Democrats’ televised debate in New Hampshire on Saturday as Sanders fights for the nomination against Clinton, the party’s front-runner.

CBS News cited a Democratic election source as saying the Sanders campaign would be denied access to the DNC files, which contain voter information such as past support and donation history, until the campaign explains its actions. The campaign also will have to provide proof that the data obtained during the breach has been disposed of.

“We are also looking at the option of an independent audit by a data security firm,” the source added.

Sanders’ campaign told NBC none of the accessed data had been downloaded or printed.

(Reporting by Susan Heavey; Additional reporting by Megan Cassella; Editing by Bill Trott)