Singapore will "spare no effort" to track down and bring to justice those who threaten to attack the Republic's computer networks, said Prime Minister Lee Hsien Loong on Wednesday.

In his first comments after hacktivists threatened to cripple Singapore's IT infrastructure last week, Mr Lee said such threats are not "a laughing matter".

"It is not just anything goes and you are anonymous, therefore there is no responsibility," PM Lee told reporters after viewing security forces in a counter-terrorism exercise, codenamed Highcrest.

He added: "You may think you are anonymous. We will make that extra effort to find out who you are."

PM Lee noted the Internet and communications networks have become an "essential part" of life and business. "Therefore when somebody threatens to do harm to it, to bring it down, to knock it out, we take that very seriously and we will spare no effort to try and track down the culprits.

"And if we can find him, we will bring him to justice and he will be dealt with, severely."

Last Thursday, global hackers group Anonymous issued its threat to protest recent licensing regulations on news sites. The group posted a YouTube video of someone in a Guy Fawkes mask, urging Singaporeans to mount a protest on Tuesday as well.

PM Lee said the Government was beefing up its systems to make it difficult for cyberhackers, though he cautioned it was not possible to be "100 per cent waterproof" because IT systems are complicated and "somewhere or other, there will be some weakness which could be exploited".