All computers used officially by public servants in Singapore will be cut off from the Internet from May next year, in an unprecedented move to tighten security.

A memo is going out to all government agencies, ministries and statutory boards here about the Internet blockade a year from now, The Straits Times has learnt.

There are some 100,000 computers in use by the public service and all of them will be affected.

"The Singapore Government regularly reviews our IT measures to make our network more secure," a spokesman for the Infocomm Development Authority (IDA) said when contacted.

The move is aimed at plugging potential leaks from work e-mail and shared documents amid heightened security threats.

Trials started with some employees within the IDA - the lead agency for this exercise - as early as April. Web surfing can be done only on the employees' personal tablets or mobile phones as these devices do not have access to government e-mail systems. Dedicated Internet terminals have been issued to those who need them for work.

The Straits Times understands that public servants will be allowed to forward work e-mails to their private accounts, if they need to.

It is rare even for banks, telcos and casinos - which are known to have the strictest computer-use policies - to cut off Internet access on all work terminals.

Banks give only some personnel - such as analysts, sales staff and corporate communications employees - Internet access, but file-sharing, Web-hosted e-mail and pornography websites are blocked. The fear is that staff may download malware accidentally from dodgy websites, or share sensitive documents online.

Mr Aloysius Cheang, Asia-Pacific executive vice-president of global computing security association Cloud Security Alliance, said the Government's move marks a return to the past - the 1990s - when Internet access was available only on dedicated terminals.

"In the past, it was hard for malware to extract sensitive information from within government networks," he said. "Now, it is hard to control any leak on social media or file-sharing sites."

It will take time to convince users about the new system as the Internet is ingrained in most work processes. One teacher noted that he uses it extensively to develop worksheets and test papers.