A cyberattack on Singapore’s public health system has compromised data from 1.5 million people, including Prime Minister Lee Hsien Loong, a cancer survivor, the authorities announced on Friday.

“This was a deliberate, targeted and well-planned cyberattack,” Singapore’s Health Ministry and Ministry of Communications and Information said in a statement. “It was not the work of casual hackers or criminal gangs.”

Singaporeans who visited certain outpatient clinics between May 1, 2015, and July 4, 2018, may have been affected. The target of the attack was SingHealth, which runs four public hospitals and other facilities.

The data purloined includes basic personal information: names, addresses, gender, race and birth dates. In addition, information about what drugs were dispensed in outpatient clinics to 160,000 people was exposed and copied during the hack.