Approximately 103,000 Medicare beneficiaries may have been affected by a data breach in May affecting Medicare.gov accounts, the Centers for Medicare & Medicaid Services said Monday.

Potentially accessed information included beneficiaries’ provider information, mailing address, dates of service, diagnosis codes, services received and plan premium details, according to the federal agency.

CMS said that its call center began receiving inquiries May 2 from beneficiaries who received letters confirming the creation of Medicare.gov accounts that they did not initiate.

“Following detection of the incident, CMS worked quickly to deactivate affected accounts, assess the scope and impact of the compromise, and mitigate the effects on impacted individuals,” the agency said. “CMS is working closely with appropriate parties to investigate this situation.”

CMS also said it disabled the ability to create new Medicare.gov accounts from foreign internet addresses to prevent further exploitation and is monitoring claims data for any suspicious activity. Affected individuals are receiving new Medicare cards with new Medicare beneficiary identifiers.

CMS has informed beneficiaries of the breach and the steps the agency is taking to mitigate any damage, along with steps individuals can take to protect their privacy. “Your current Medicare benefits or coverage aren’t affected by this incident,” the agency stressed in the letter.

The agency encourages all beneficiaries to review all notices and explanations of benefits for any unfamiliar charges or services. Additionally, CMS said, beneficiaries should report any suspicious activity to 1-800-MEDICARE (1-800-633-4227) or the Office of Inspector General.