An estimated 18,000 current and former members of Hawaii Medical Service Association had their personal information stolen during a cyber attack on Anthem Inc., a Blue Cross and Blue Shield plan that serves residents in 14 states. 

HMSA, the state’s largest health insurer, said in a post on its website that the number of affected members could increase as it processes about 2,000 unknown names in Anthem’s database to determine if they are or were HMSA members. The data stolen from Anthem was for a 10-year period from 2004 to 2014.

“I’m deeply concerned about the cyber attack and the impact on HMSA’s members,” Mike Gold, HMSA’s president and chief executive officer, said in the post. “We’re sending letters to current and former members who are affected. Anthem is also sending affected HMSA members a letter over the next few months.”

HMSA said information may have been breached for members who have had an Anthem plan in the last 10 years or had services in states where Anthem operates. 

The insurer said it typically doesn’t share Social Security numbers, email or street addresses, telephone numbers, medical or financial information or other private information. 

“The only information that Anthem has on HMSA members would have been provided by a doctor or hospital in an Anthem state that cared for an HMSA member,” Gold said. “This would include those members’ names, dates of birth, the cities and states where they live, and part of their HMSA membership number after it processed out-of-state medical or hospital services.”

Anthem operates Blue Cross and Blue Shield health plans in California, Colorado, Connecticut, Georgia, Indiana, Kentucky, Maine, Missouri, Nevada, New Hampshire, New York, Ohio, Virginia, and Wisconsin. 

For more information, call HMSA at (808) 948-6699 on Oahu or (800) 432-6633 toll-free on the neighbor islands and the mainland. The hotline is open Monday through Friday from 8 a.m. to 5 p.m.