"Information on the outpatient dispensed medicines of about 160,000 of these patients was also exfiltrated".
The data stolen from SingHealth's database consists of names, addresses, gender, national registration number, race and date of birth. It added that all patients who had visited healthcare institutions under SingHealth would receive SMS notifications informing them of the security breach.
The data breach exposes almost 1.5 million people who may have visited hospitals between May 2015 and July 4, 2018.
"Singapore ranks among the leaders in cyber security, and we would like to see more governments follow its lead in disclosing breaches".
"We are convening a Committee of Inquiry to look thoroughly into this incident", he said.
While officials refused to comment on the identity of the hackers citing "operational security", experts told Agence France-Presse that the complexity of the attack and its focus on high-profile targets like the prime minister pointed to the hand of a state-actor.
Authorities first noticed unusual activity in one of SingHealth's IT databases on July 4, according to the Health Ministry's news release.
According to preliminary data, the computer system of one of the two largest public health departments in SingHealth was infected with malware that allowed hackers to take over the database.
Meanwhile on 12 July 2018, a police report was made, with investigations ongoing.
As a result of the hack, IHiS has been instructed to do a thorough review of the public healthcare system in an attempt to prevent future hacks from taking place. "These include temporarily imposing internet surfing separation" on all of SingHealth 28,000 employees, authorities say.
"Many businesses and governments in Southeast Asia face cyber threats, but few recognise the scale of the risks they pose".
SingHealth said no phone numbers, financial information or other patient medical records were illegally accessed.
In his Facebook post about the attack, Lee warned that "those trying to break into our data systems are extremely skilled and determined".
The incident also highlights the fact that networks and endpoints can no longer be trusted, said Kyne, because attackers will inevitably find a way in.
During the press conference on Friday, Health Minister Gan Kim Yong called this attack "unprecedented" and apologised to those affected patients. They only need to succeed once to gain a foothold, and when they can't be detected and stopped before they complete their mission, we need to go back and assess how they succeeded and evaluate the security strategy. PM Lee assured that the hack is not going to be a setback in the digitization of health records, but a motivation to build a "secure and smart nation".