Hackers could have in their possession taxpayer information from the S.C. Department of Revenue that would allow crooks to take over bank accounts, file for bogus tax refunds or get fraudulent loans, national data security experts said Monday.

“This is about the worst you can get,” said Avivah Litan, an ID theft analyst with the information technology research group Gartner. Added Rick Holland, an analyst with Forrester Research, “If I were a resident of South Carolina, I would be pretty concerned.”

S.C. leaders are trying to resolve a cyber attack affecting four times as many people as all previous S.C. data breaches in the past seven years.