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The state of Massachusetts is warning 150,000 members of its Prescription Advantage insurance program that their personal information may have been snatched by an identity thief.

Local authorities arrested a lone identity thief in August who had been using information taken from the program in an attempted identity theft scheme, said Alison Goodwin, a spokeswoman for the state's Executive Office of Health and Human Services.

Goodwin could not add many details on the nature of the breach, citing an ongoing criminal investigation, but she said Prescription Advantage is conducting an internal review of the incident to determine if additional security measures might be required.

Prescription Advantage is a state-run program that offers drug insurance to seniors in Massachusetts. The data breach did not affect all members of the program, Goodwin said.

Although the thief used information from just a small number of participants in the scheme, state data-breach laws require that the 150,000 people who could have possibly been affected by the breach be contacted.

Prescription Advantage has been doing that over the past week via postal mail.

"A few members were recently the victims of attempted identity theft," the state said in a Nov. 19 letter sent to possible victims. "Prescription Advantage is fully cooperating with law enforcement authorities in their ongoing investigation of this matter."

The staff that maintains the program has "no reason to believe" that any Prescription Advantage members' data has been misused, the letter adds.

Members who have questions about the breach can call Prescription Advantage during regular business hours: 1-866-523-6846 or 1-877-610-0241 for those who are hearing impaired.