He worked for the National Library Board (NLB) for six years and had access to its database, which contained the personal information - such as NRIC numbers and contact details - of its 2.4 million members.
Project manager Ang Boon Sin, now 39, repeatedly abused his position, gaining access to the Spydus database to retrieve data on at least 180 NLB members for an unlicensed moneylender known only as Johnson.
He was jailed for three years and eight months, and fined $270,000 yesterday after pleading guilty to 10 counts of gaining unauthorised access to computer material, nine counts of assisting an unlicensed moneylender and one count of removing benefits of Johnson's criminal conduct from Singapore.
He committed these offences in 2015; 463 other charges for similar offences were taken into consideration during sentencing.
Deputy Public Prosecutor Marcus Foo said Ang had had financial difficulties since 2001 andlater borrowed $5,000 from Johnson that he was unable to repay.
DPP Foo added: "Some time in March 2015, Johnson made the accused an offer to work as his runner. In return, a portion of the accused's debts would be waived in that he would no longer need to pay the weekly interest of $2,500, but the remaining $1,000 monthly for a period of 10 months."
Ang accepted the offer and helped the loan shark.
His tasks included creating a website advertising Johnson's illegal business, producing unlicensed moneylending advertisements with graphics, collecting cash from Johnson's runners and making cash deposits.
Johnson also told Ang that he wanted his debtors' contact numbers and updated addresses, so that he could send his runners to them or call them up should they become uncontactable.
He also wanted the particulars of neighbours and employers of his debtors that he could use to track their whereabouts.
DPP Foo said that to date, the authorities have not established Johnson's true identity.
Before handing out the sentence, District Judge Wong Li Tein said Ang's offences could send "a chill down the spine" of NLB members, who make up almost half of Singapore's population.
Stressing that he could have exposed their personal information to loan sharks, she added that he had done the NLB a "great disservice".