The Democratic National Committee has told the campaign of Senator Bernie Sanders of Vermont that it was suspending its access to its voter database after a software error enabled at least one of his staff members to review Hillary Clinton’s private campaign data.
The decision by the party committee is a major blow to Mr. Sanders’s campaign. The database includes information from voters across the nation and is used by campaigns to set strategy, especially in the early voting states.
The breach occurred after a software problem at the technology company NGP VAN, which gives campaigns access to the voter data. The problem inadvertently made proprietary voter data of Mrs. Clinton’s campaign visible to others, according to party committee officials.
The Sanders campaign said that it had fired a staff member who breached Mrs. Clinton’s data. But according to three people with direct knowledge of the breach, there were four user accounts associated with the Sanders campaign that ran searches while the security of Mrs. Clinton’s data was compromised.
The Washington Post first reported the issue.