University of California San Diego's (UCSD) Moores Cancer Center has sent a letter to 30,000 patients, after a hacker breached its computers and gained access to patients' personal information, according to a report in the San Diego Union Tribune.

The letter, dated July 9, was sent as a precaution to inform patients that the facility's computers were compromised on June 26, according to DeAnn Marshall, UCSD Health Sciences' chief of marketing and communications officer.

The computer servers affected contained information such as patients' names, dates of birth, medical record number, diagnosis and treatment dates back to 2004, Marshall told the Tribune. She added that the vast majority of patients' information did not include Social Security numbers.

She also said there is no evidence that any of the information has actually been viewed or used. Patients' medical records, which are stored in separate servers, were not breached, according to the cancer center.

Marshall said authorities have been notified, and an investigation is under way.