In a letter posted on the bank's Website, DBS Ceo Piyush Gupta, says the outage was triggered during a routine repair operation on a component within the disk storage subsystem connected to the bank's mainframe.
"So far, we understand from IBM that an outdated procedure was used to carry out the repair," says Gupta. "In short, a procedural error in what was to have been a routine maintenance operation subsequently caused a complete system outage."
IBM and BDS entered into a S$1.2bn agreement in 2002 in which the bank outsourced IT services and infrastructure in Singapore and Hong Kong to IBM.
Gupta says that all payments and transactions that were scheduled to be made on 5 July were completed. "Nothing was held over and full data integrity was maintained at all times," he says.
He continues: "I am treating this matter with utmost priority and the full scale investigation that we initiated last week is still underway. This investigation is being done with the support of IBM's labs in the US and their engineering teams in Asia.
In a statement, IBM says it has taken steps "to enhance training of our personnel related to current procedures and brought in experts from our global team to provide further assistance."
In addition, IBM and DBS are taking "additional actions to increase the resiliency and redundancy of this part of DBS' infrastructure."