Singapore Prime Minister Lee Hsien Loong called Thursday for stronger Southeast Asian cooperation against cyber threats after his own website was hacked by critics demanding greater Internet freedom. "I do not think any country has been spared. So we have to strengthen our defences and cooperate to deal with these common threats," he told a conference of regional telecommunication and information-technology ministers. He said websites in Thailand, the Philippines, Malaysia and Indonesia had also been "compromised" and vowed to prosecute culprits in Singapore "to the full extent of the law". Five Singaporeans are being questioned on suspicion of hacking the websites of the prime minister and the president last week. Lee's official website was hacked by apparent members of global activist group Anonymous demanding that Singapore rescind recent rules requiring news websites to obtain annual government licences, which critics see as an attempt to curtail online press freedom. "We must not condone such malicious and harmful behaviour. It is not a prank when someone hacks websites and intrudes into computer systems. It is in fact, a criminal act," Lee said. "At a minimum it inconveniences the public, but potentially it has much graver consequences. It can damage infrastructure and endanger lives. For example, if the computer systems hacked control the electricity grid, or the water supply, or a hospital management system, or a banking system." Experts told AFP after a recent spate of attacks in Asia that hackers can use weaknesses in one country to intrude into a better-protected information system in another. They called on governments and businesses to update cyber security defences against increasingly sophisticated threats.