The Monetary Authority of Singapore has ordered DBS and Citibank to investigate why it took so long to get their systems back up after an outage earlier this month that disrupted online and payment services.
Between the afternoon of 14 October and the following morning, DBS and Citibank customers were unable to access apps and online banking as well as payment services such as PayLah! and PayNow. ATMs were also down at some locations.
The outage was caused when a planned upgrade at a data centre was hit by a problem with the centre's cooling system, according to provider Equinix.
The banks activated their back-up data centres but systems were not fully recovered within the four-hour timeframe required by the regulator.
MAS says that while it does not have oversight of data centres, it expects banks to establish contractual agreements with providers that incorporate MAS’ requirements on system availability.
The regulator has ordered the banks to conduct a thorough investigation on why they were not able to get back online within four hours, and will take "appropriate supervisory actions after gathering the necessary facts".
In May, Singapore's central bank mposed additional capital requirements on DBS, following widespread outages in March and a subsequent disruption to its digital banking and ATM services two months later.