The Internet is the greatest single source of information in the world but it is not always the best if you need accurate medical help, according to researchers in the United States.

Scientists at the University of Michigan set themselves the task of finding out about a particular kind of bone cancer, including available treatments, using the Internet.

They found that nearly half the available websites had not been checked by doctors, while some gave the wrong advice altogether.

Looking up the word cancer on the Internet will bring up more than three and a quarter million web pages on the subject. Even looking for something more specific, such as particular diseases like breast cancer or leukaemia, can turn up tens of thousands of websites.

'Gross inaccuracies'

Biermann: Half the pages irrelevant

The scientists at the University of Michigan narrowed their study to websites devoted to Ewing's sarcoma, a rare bone cancer.

"Half of the pages we retrieved weren't even relevant to the disease. Some 40% actually had not been through any kind of scientific scrutiny before it was put on the Internet," said the study's leading researcher, Dr Sybil Biermann.

Other websites contained what Dr Biermann calls "gross inaccuracies", including claims by health food retailers that their products could cure bone cancer.

One site claimed that Ewing's sarcoma is almost always fatal, when in fact, three out of four people who develop it survive.

Dead ends

Dr Biermann says her team were also frustrated by hundreds of Internet dead ends - websites with no medical information at all.

Biermann: Internet can help patients

As most people have to pay for time they spend on the Internet, those dead ends can be expensive as well as irritating.

But Dr Biermann still believes the Internet can help many patients, especially people who live a long way from their nearest doctor or hospital.

"The Internet can be a very powerful tool, and I actually encourage patients to use the Internet but I try to direct them and to make it more helpful for them," she said.

"I give them websites that I've reviewed that I feel have helpful and credible information. So for example if they do a search that they're actually searching for the correct information and that what they get will be relevant to their care."