The Democratic National Committee has suspended Bernie Sanders’ access to the party’s 50-state voter file in response to a software glitch that allowed the Sanders campaign to access Hillary Clinton’s internal voter data.

The DNC move effectively freezes Sanders’ field organizing program six weeks from the first caucuses and primaries.

The breach occurred on Wednesday, a DNC official confirmed, through the NGP VAN, the leading technology company that allows campaigns to identify voters, as well as monitor their preferences and leanings, in what’s called the 50-state voter file. For a “brief window” — about 30 minutes, an official said — a bug in the software exposed the campaigns’ internal “voter ID” data.

During that period, the Sanders campaign discovered the breach, accessed the Clinton campaign’s data, then called the vendor to point out the flaw, according to the official. The DNC has since cut off Sanders’s access to the voter file — until his campaign officials can “prove” they’ve deleted the Clinton data.