9. 21st Century Oncology
In March, 21st Century Oncology, a Fort Myers, Fla.-based cancer care provider, announced that a data breach had exposed the information of 2.2 million patients based across all 50 states and internationally. Hackers broke into a company database in October 2015, the company said, accessing personal information of patients, including names, Social Security numbers, physician names, diagnosis, treatment data and insurance information. The company said it had "no indication that the information has been misused in any way."