Investigations are underway after the medical records of some American football players at the University of Iowa (UI) were accessed.
A review of the UI Hospitals and Clinics' electronic records system flagged up the breach, which could have led to data loss.
The incident involves 13 athletes who were admitted to the hospitals with rhabdomyolysis, although it is unknown whether all men's data were accessed.
Medical records are supposed to only be accessed by healthcare workers with legitimate grounds to view them, and there is reason to believe that this was contravened.
In a statement, the university said: "The players and their families were notified of the possible violations today.
"The patients will receive letters that will detail the outcome of the investigation, which may take up to two weeks."
According to a recent survey by the Information Commissioner's Office, 80 per cent of people are concerned that their personal information is not adequately protected online.