The world’s most popular search engine, used by 90 million people every month, has been asked to hand over an entire week of search requests made at Google.com.

The US Department of Justice wants the information to help it to establish how much child pornography is available on the internet, but Google is unhappy that it is being used as part of what it calls a “research experiment”. Although the contents of most searches are anonymously entered phrases such as “weather in Rome”, some could reveal personal information.

Google has now been taken to court in California by Alberto Gonzales, the US Attorney-General. The lawsuit describes any privacy concerns as illusory, arguing that it does not want to see “any additional information that would identify the person who entered the search”.

Other search engines, such as Yahoo! and AOL — which use Google technology — have complied with the request, although it is not clear what they handed over. Google was originally asked to hand over every search made between June 1 and July 31 last year.

The site’s lawyer said: “Google’s acceding to the request would suggest that it is willing to reveal information about those who use its services. This is not a perception that Google can accept.”

Opinion on whether Google is right to resist is divided. John Carr, an internet adviser to NCH, the children’s charity, said: “This is a morally bankrupt argument. They seem to be saying, ‘If we give them this, what’s going to be next?’ when you should be judging each case on its merits.”

One US influential privacy group backed Google, but expressed concern about the amount of information that the company retains. The search engine logs all the searches made, which computer they came from and what technology was used to make the search. Kevin Bankston, an attorney for the Electronic Frontier Foundation, an organisation that promotes the freedom of the internet, said: “The only way Google can reasonably protect the privacy of its users from such legal demands now and in the future is to stop collecting so much information.”

British authorities have not made any similar blanket requests for search engine data, although Google is understood to be willing to comply with specific police requests. All search engines in Britain subscribe to a Home Office code, which recommends that they “seriously consider” blocking weblinks that contain illegal child abuse images.

Google has described the US Government’s demands as “overbroad, unduly burdensome, vague and intended to harass”. At its Silicon Valley headquarters, the company displays a list of live search terms that can be seen by visitors.

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