Sir, - I strongly suspect that your leading article (September 2nd) missed the point when it came to the Exon Act and other attempts to limit what goes on the Internet. In essence, the Act says that Internet Service Providers (ISPs) are liable if anyone who uses their service succeeds in upsetting someone else in America by posting or forwarding material of a sexual nature. It also implies that an ISP is liable if someone is offended by material of a sexual nature while using the ISP's service, regardless of where that material is found.

This legislation is monstrously flawed, for a number of reasons. For a start, the ISP will in theory have to monitor all incoming and outgoing traffic. This is like asking Telecom Eireann to tap every phone line in the country in case someone says something of a criminal nature. Unlike the phone system the Internet doesn't just carry messages. Diagrams, images and sometimes sound travel the Internet in a variety of digital formats. Thanks to Mr Exon, an ISP will now have to track every large digital object, figure out what it is and decide if it's offensive.

Monitoring traffic is also pointless, as good encryption software is now widely available. Although messages can be decrypted the process can take weeks of computer time per message. And if the ISP fails to decrypt a message which is later successfully decrypted by a third party who finds it offensive then another court case will beckon.

Even if the service provider complies with the Act and somehow manages to stay in business, all that will happen is that people who disagree with the Exon Act will use a service provider in a country that doesn't have its own similar legislation.

This Act is the thin end of a long and nasty wedge. The same shady figures who backed Exon are no doubt planning another Act. What'll be banned next time? Flag burning? Anything to do with Cuba or Iran? Blasphemy? At what point in the erosion of our right to Freedom of Speech do we stop? - Yours, etc.,

San Francisco.