The breach compromised personal data of 1.5 million SingHealth patients. The incident also compromised outpatient medical data of 160,000 patients that visited the healthcare provider's facilities, which included four public hospitals, nine polyclinics, and 42 clinical specialties. The attackers used a publicly available hacking tool to breach an end-user workstation. The workstation was running a version of Microsoft Outlook that was not updated with a patch to address the use of the hacking tool.

Hackers broke into SingHealth's IT systems to steal the data of 1.5 million patients and records of the outpatient medication given to Prime Minister Lee Hsien Loong. The attackers specifically and repeatedly targeted Mr. Lee's personal particulars and information on his outpatient dispensed medicines. The hackers first broke into SingHealth's IT system via a front-end workstation, and later managed to obtain log-in details to assess the database Data compromised included name, NRIC number, address, gender, race, and date of birth of 1.5 million patients.