US-based hospital system UCLA Health has been hit by a cyber attack, where hackers accessed parts of the computer network that include personal and medical information.
UCLA Health said it currently has no evidence whether the cyber attacker actually accessed or acquired any individual’s personal or medical information.
Conceived to be the work of criminal hackers, the cyber attack is expected to involve the data of 4.5 million individuals.
UCLA Health is working with investigators from the Federal Bureau of Investigation (FBI) to solve the issue and hired private computer forensic experts to further secure information on network servers.
UCLA Hospital System president Dr James Atkinson said: "Our patients come first at UCLA Health and confidentiality is a critical part of our commitment to care.
"We sincerely regret any impact this incident may have on those we serve. We have taken significant steps to further protect data and strengthen our network against another cyber attack."
UCLA Health found suspicious activity in its network in October 2014 and started an investigation with the help of the FBI.
In May, the hospital system determined the attackers accessed parts of its network, which comprise personal information such as names, addresses, dates of birth, social security numbers, medical record numbers, Medicare or health plan ID numbers and medical information.
UCLA Health operates four hospitals on two campuses, including Ronald Reagan UCLA Medical Centre, UCLA Medical Centre of Santa Monica, Mattel Children’s Hospital UCLA and Resnick Neuropsychiatric Hospital at UCLA.
It also has 150 primary and speciality offices throughout southern California.