INDIANAPOLIS — The theft of a computer server may have exposed Social Security numbers and other personal information of as many as 700,000 people.

The information containing customer-billing records for about 100 Indiana businesses, including St. Vincent Health system and Methodist Medical Group, was on a server stolen last month from a debt collection agency.

The data was limited to past-due billing information that had been turned over for debt collection to the Central Collection Bureau, the agency said Friday. The bureau collects overdue bills on behalf of dozens of Indiana businesses, including doctors and hospitals.

“We’re obviously heartsick about this,” said Chet Klene, Central Collection Bureau president. “We’ve been in business since 1972, and nothing like this has ever happened before.”

The server was stolen March 21. The information was protected by two passwords but was not encrypted, Klene said.

“Our server was password protected. We have obviously spoken to some IT people who feel that a good computer hacker could get through those passwords,” he said.

Police have not found the missing server, and the collection agency has notified companies whose billing records were compromised, Klene said.

“But obviously we need to be notifying those that could have potentially had information on there. We are recommending that they put credit freezes on or at least monitoring on their credit reports,” said Klene.

Some of the information might be outdated. St. Vincent Health System said it had not given any billing business to Central Collection in more than three years, so all of the missing billing information is several years old.

The data also included past due billing statements for 51,000 former Citizens Gas customers, including names, last known addresses and Social Security numbers. The data was on customers the utility had not been able to find on its own, spokesman Dan Considine said.

“We certainly take this very seriously, any time there is a security breach, and we hope it gets cleared up very soon,” he said.

The Indiana attorney general’s office also is investigating the theft.