The personal information of 612,000 Medicare beneficiaries were accessed in a sweeping data breach that affected what could be hundreds of organizations, including the government contractor, Maximus Federal Services.

The Centers for Medicare & Medicaid Services (CMS) announced in a press release Friday that it is notifying people affected by the data breach, which could have affected information including beneficiaries, names, Social Security numbers, medical histories, diagnoses and other personal details.