The Democratic National Committee has told the presidential campaign of Bernie Sanders that it is suspending access to the DNC voter database after at least one of Sanders’ staff members reviewed Hillary Clinton’s private campaign data.

The New York Times writes a software error inadvertently made proprietary voter data of Clinton’s campaign visible to others. The Sanders campaign said it has fired a staff member who breached Clinton’s data, the Times reported. But, the Times wrote, there were four user accounts associated with the Sanders campaign that ran searches while the security of the Clinton data was compromised. Clinton, the front-runner for the Democratic presidential nomination, and Sanders are scheduled to debate on Saturday.