The US Supreme Court has upheld the decision that an ISP cannot be held responsible for content posted through its services.

The New York Appeals Court ruled in December that ISP Prodigy was not liable for an impostor opening accounts under another name.

Six years ago, an impostor opened an account with Prodigy under the name of a 15-year-old boy and posted obscene bulletin board messages and threatening emails. The boy's father launched a liability lawsuit against the ISP, but the New York Court of Appeals rejected the claims.

The New York court ruled that Prodigy could be not held responsible because it could not be treated as the publisher of the messages - only as a telephone company.

This ruling has now also been upheld by the US Supreme Court, according to reports.

In the UK, however, an ISP is regarded as a publisher and would be found liable for content posted on its services. Earlier this year, ISP Demon decided to pay damages to academic Laurence Godfrey who claimed it had hosted "squalid, obscene and defamatory" material about him.

Demon said its case raised questions over whether service providers should be held responsible for defamatory message posting, even if they have not been warned to remove them.