Standard Chartered has revealed that 647 wealthy clients' confidential bank statements were stolen in Singapore, from a printing company.
The statements, stolen from Fuji Xerox which was hired to print statements for all those clients, were found on alleged hacker James Raj Arokiasamy's confiscated laptop, the city's police said.
The London-based lender also said it had not found any unauthorised transactions since the theft occurred.
News of the theft weighed down on Standard Chartered's stock price, which dropped 2.76% to HK$169.30 in Hong Kong, its lowest in five months.
Meanwhile, Singapore's central bank said it could take regulatory action against the London-based lender after it examines the bank's investigation into the theft.
Arokiasamy's lawyer, M Ravi, refused to comment, reported Bloomberg.
"This incident will raise questions about Standard Chartered's ability to deal with client data," Ronald Wan, chief China adviser at Asian Capital Holdings told the news agency.
"Regulators and financial institutions need to think about whether there should be more stringent oversight and requirements on third-party service providers," he added.
The Monetary Authority of Singapore (MAS) is "actively engaging" with Standard Chartered on the theft, which is an isolated case, the central bank said.
"Globally, financial institutions have been facing an increasing number and variety of cyber threats," the central bank said in a statement on 5 December.
The theft "underscores the need for heightened vigilance, including close management of risks pertaining to service providers", MAS added.
Client's data was stolen from a server used for Standard Chartered Private Bank at a printing facility, Fuji Xerox Singapore chief executive Bert Wong said in a statement on 5 December. Other clients were not impacted and a forensic team is investigating the breach, Wong added.
The security breach threatens to dent Singapore's standing as a safe private-banking hub for Asia.
The city-state, Asia's largest wealth management center, handles about $800bn (£489bn, €585bn) in offshore assets, according to the Boston Consulting Group (BCG).
About 8.2% of all households in the city-state hold assets of $1m or more, making it the fifth-largest fraction behind Qatar, Switzerland, Kuwait and Hong Kong, BCG said in May.