The national pension system has been hacked, leading to 1.25 million cases of personal data being leaked, the Japan Pension Service announced Monday.

In a scandal reminiscent of the nation’s botched handling of pension records about a decade ago, people’s pension IDs, names, addresses and birth dates have been stolen through illicit accesses to fund workers’ personal computers, fund officials said.

The data were leaked when agency employees opened an attached file in their email containing a virus.

Japan Pension Service President Toichiro Mizushima apologized for the leak and said affected people will be given new pension ID numbers.

“We feel an extremely grave responsibility over this,” Mizushima told a hastily arranged news conference. “We will make the utmost efforts not to cause trouble to our customers.”

The hacked computers were not connected online to the fund’s core computer system, which keeps financial details of the pension system’s members, officials said. No illicit access to the core system, which contains the most sensitive information, such as the amount of premiums paid by and the amount of benefits paid to each individual, has been detected, they said, adding that they are still investigating the incident.

There is a possibility that the perpetrators changed the addresses of the individuals using the stolen data, the officials said.

Of the 1.25 million cases, some 52,000 involved the theft of pension IDs, names, birth dates and addresses, while another 1.17 million involved the leak of just pension IDs, names and birth dates. In the remaining 31,000 cases, just pension IDs and names were stolen.

The officials have removed infected PCs from the LAN system they had been connected to. Pension employees are now denied access to the Internet from their offices.

Mizushima said the fund reported the attacks to the Metropolitan Police Department on May 19. He refused to elaborate on the type of computer virus or whether the attacks came from within Japan or abroad, citing the ongoing police investigation.

The fund officials also acknowledged that, regarding some 500,000 of the 1.25 million cases, passwords were not set, in an apparent violation of the fund’s internal rules.

People who have received suspicious calls or mail are urged to call the Japan Pension Service at 0120-818211. The operators are available from 8:30 a.m. through 9 p.m.

Public outrage over botched record-keeping that left millions of pension premium payments unaccounted for was a major factor in a devastating defeat suffered by Prime Minister Shinzo Abe’s Liberal Democratic Party in the 2007 Upper House election.

Abe, whose first Cabinet also lost several ministers to other scandals and gaffes resigned in September of that year in the face of Diet deadlock and health problems.

Information from Reuters added