A former convict has been identified as the perpetrator.
In a country where homosexuality is technically illegal, a recent online security breach of 14,200 people and their HIV positive statuses have LGBT advocates concerned.
Details of patients including names, ID numbers, phone numbers, and addresses were leaked according to CNN.
Private information was made available on 5,400 Singaporeans diagnosed as HIV-positive before January 2013 along with 8,800 foreigners diagnosed before December 2011, the Ministry of Health (MOH) said in a statement.
The MOH identifies Mikhy K Farrera Brochez, a US resident who lived in Singapore until May 2018, as the person in possession of the confidential registry.
"We are sorry for the anxiety and distress caused by this incident," the statement said. "Our priority is the wellbeing of the affected individuals. Since 26 January, we have been progressively contacting the individuals to notify them and render assistance."
Brochez was deported in May 2018 after serving time in prison on fraud charges when it was discovered he lied about being negative to live in the country. HIV-positive foreigners cannot receive employment visas or permanent residence status.
The LGBT charity organization Oogachaga, says they are concerned that employers, families, and friends may take the information and use it against people who have not disclosed their statuses.
"This reminds us of the insufferable stigma, fear and discrimination that continues to surround people living with HIV in Singapore today," Leow Yangfa said speaking on behalf of Oogachaga. "Those of us who live without HIV cannot begin to imagine the shock, distress, pain and betrayal they must be going through right now."
Authorities will heavily prosecute anyone found sharing the data.
"Police will not hesitate to take stern action, including prosecution, against those who have breached the OSA. A person found guilty of the wrongful possession, communication or use of confidential data shall be liable to a fine not exceeding S$2,000 [roughly $1,500 US], and to imprisonment for a term not exceeding two years," a police statement said.