Berkeley Fire Department has notified more than 900 Berkeley ambulance patients that a Tampa-based tax fraud ring may have fraudulently accessed and used some of their personal information.

There is forensic evidence that a now-terminated employee of Advanced Data Processing Inc. — the company that handles billing for Berkeley’s fire department and ambulance services — accessed client information with the intention of providing it to a tax fraud ring based out of Tampa, Deputy Fire Chief Gil Dong said.

The information accessed — and in some cases disclosed to an unauthorized third party — may include names, social security numbers and dates of birth, according to a press release from ADPI. No medical information was accessed or disclosed.

Thirteen suspects have been arrested for their involvement with the ring responsible for the Berkeley information theft, according to a press release from Tampa Bay Police Department.

The tax fraud ring that accepted the information from the ADPI employee is suspected of filing fraudulent tax returns with the Internal Revenue Service, according to the ADPI release.

The Internal Revenue Service declined to comment.

The fire department initially sent out 168 letters notifying patients of the possible access before new forensic evidence prompted it to send a second round of letters to an additional 763 customers in conjunction with ADPI, Dong said.

ADPI has now taken steps to strengthen its internal security procedures by inviting outside auditors and experts to observe its operation, Dong said.

“It takes an intentional act to take the information,” Dong said. “They had an employee who was involved in taking that information. They were able to go through and look at forensic evidence to see what computers had been accessed.”

Despite this breach, Berkeley Fire Department has no plans to change its practices.

“We use an ambulance billing vendor because they have the expertise in filing for Medicare and medical and health insurance reimbursement,” Dong said. “We don’t have the internal expertise, and we have been using billing vendors for over 20 years without incident.”

All patients affected by the breach have been offered a year of free credit monitoring by ADPI, and the company is cooperating with the IRS in its investigation.