THE staccato clatter of computer keys clicking all over Singapore this week signalled the hurried emptying of hard drives of any material that might transgress the republic's laws on pornography. The sudden round of electronic spring cleaning was prompted by the conviction of 41-year-old Lai Chee Chuen on 77 charges of having obscene films, downloaded through the Internet, as well as a collection of obscene CD-ROMS and magazines. Coming only days after Singapore went live with its drive to clean up the Net of material regarded as pornographic, racist or seditious, it concentrated wonderfully the minds of all those who might have been surfing about in search of prurient material. Yet the Lai case was not an example of the watchdogs prowling around at random. The arrest, made in July last year, followed intensive work by Interpol as part of a probe into child pornography rings using the Internet to exchange information and images. Other suspicious sites were identified in Hong Kong, Britain, Canada, Germany and South Africa. Once supplied with Lai's log-on - faithfully reproduced by the Straits Times so well-wishers could get in touch with him - the local Commercial Crime Division monitored him, and finally raided his home. The fact that Lai, who was fined S$61,500 (HK$334,160), was a special case has not calmed fears of Singaporeans who are concerned that, government assurances to the contrary, Big Brother really might be watching them. How the police were able to monitor Lai's activities was not revealed. Local computer experts suggested that, armed with the log-on, the police could have enlisted the local Internet service providers to assist in the operation, but it was emphasised by the Singapore Broadcasting Authority that there was no regular tracking of subscribers. Nevertheless, surfers were looking for clarification on whether merely looking at pictures constituted an offence. Downloading and storing could be seen as a deliberate flouting of Singapore's pornographic laws. And what shocked many Internet users was the fact a picture and other graphics remain stored in their computers when the original file has been closed. The system used by most Web-browsers means that the images are still lurking in the hard drive, unless users regularly clear them out. Reassurances that there would be no excessive intrusion into private habits came from all sides this week. The Minister for Information and the Arts, George Yeo, said Singapore was only concerned about the broadcasters, not the receivers, and had no intention of setting up a battalion of censors to cover the Net.