By Jane Wakefield
BBC News Online technology staff
Children at a secondary school in Bradford got a little more than they bargained for when an innocent classroom search linked to pornography.
Children were not able to access the porn sites listed
The teenagers were using the Ask Jeeves' UK-based search engine to look for information on the heart during a biology lesson.
The links to hardcore pornography appeared because of a matching error between the keyword and the results, said Ask Jeeves.
The fault has now been rectified.
Ruth Whitehead, Head of Science at the Hanson Secondary School, was teaching a biology lesson to a group of sixth formers two weeks ago when the problem occurred.
"One of the girls called me over and we were both shocked at what we saw," Miss Whitehead told BBC News Online.
"It was fortunate that it was a sixth-form group. If it had been a group of 11-year-olds it would not have been good," she said.
According to Ask Jeeves' director of product Tony Macklin, the problem came about because of a new filtering system that the company has installed.
The system identifies search terms that could lead to adult content, and triggers a warning page before the links appear.
One of the terms was the name of a porn star Tera Heart.
"It was only meant to identify the two words in combination but this one did slip through," said Mr Macklin
The system has been taken out of use while it is thoroughly tested, he said.
Filtering software installed by the school would have prevented the teenagers from accessing the sites but the list of contents was enough to make even the most knowledgeable of butlers blush.
"Basically the search term we put in has gone off on a tangent and brought up hardcore porn," explained the school's network administrator Matt Charlton.
"None of the other search engines produced such a result," he added.
The school has temporarily suspended access to ask.co.uk.
Search engines such as Ask Jeeves are used extensively in schools as an integral part of the curriculum.
Inappropriate search results remain "an industry problem" according to Ask Jeeves.
"We are the most pro-active search engine, working on ways to limit exposure to such content," said Mr Macklin.
As well as displaying a warning page when queries trigger adult content, the search engine has recently added a new "your settings" features designed to help users guard against inappropriate content.
Making sure children are not exposed to inappropriate content at home or school is a concern of government.
It has launched the Web safe initiative, of which Ask Jeeves is a member, to provide a safe environment for children on the web.