SINGAPORE (Reuters) - Cyber attackers have stolen basic personal data from about 850 Singapore national servicemen and employees in a possible attempt to access official secrets, the Defence Ministry said on Tuesday.

The ministry detected the breach this month in the I-net system that allows internet surfing using dedicated computer terminals on defense ministry and Singapore Armed Forces premises, the ministry said in a statement.

No classified military information was stored on I-net, the ministry said.

“The attack on I-net appeared to be targeted and carefully planned,” it said.

“The real purpose may have been to gain access to official secrets, but this was prevented by the physical separation of I-net from our internal systems.”

Stolen data included telephone numbers, dates of birth and national ID numbers, it said. The ministry told the Cyber Security Agency and the Government Technology Agency to investigate other government systems, but no other breaches had been detected.

Last year, Singapore kick-started a process to separate the work computers of its public servants from the internet as a defense against potential cyber attacks.

But even before that, some ministries, including the defense and the foreign affairs ministries, had been using separate systems for web surfing.