The theft occurred between January 1 and January 3, and was allegedly committed by a syndicate with knowledge of the post office's information technology (IT) system.
Department of state security spokesman Brian Dube confirmed
that the theft had occurred and that the probe had been launched.
"When a government institution is compromised, the NIA
will be involved and will offer its assistance," he told the newspaper.
Postbank currently holds over R4bn in deposits, and processes
millions of rands in social grants throughout the year.
The bank told the newspaper that none of its customers were
effected by the hacking, but declined to comment further.
The syndicate reportedly opened several Postbank accounts
across the country late last year, and during the New Year holiday period
gained access to a Rustenburg Post Office employee's computer and made deposits
from other accounts into its own.
Over the next three days, automated teller machines (ATMs)
in Gauteng, Free State and KwaZulu-Natal were used to withdraw cash from the
The incident comes three years after Postbank spent over
R15m to upgrade its fraud-detection service.
An unnamed security expert told the newspaper that serious
questions had to asked about Postbank's internal systems.
"The Postbank network and security systems are shocking and desperate need of an overhaul. This (theft) was always going to be a real possibility," the expert said.