Arizona's largest health care system is stepping up security measures after two recent cyberattacks.
Phoenix-based Banner Health announced Wednesday that it was mailing letters to 3.7 million people who may have been affected by the computer hacks.
That includes patients, health plan members, beneficiaries, food and beverage customers, physicians and health care providers.
Agency officials say it discovered one hack early last month that targeted credit card data as it passed through payment processing systems
In another cyberattack detected in mid-July, Banner Health says hackers may have gained access to patient information.
Banner Health says the hacks didn't affect all patients or health plan members.
The agency is offering a free one-year membership to a monitoring service for those whose information may have been compromised.