The five UK mobile operators have been collecting information about the websites handset users visit from their devices for the past year, as part of a trial by the GSM Association (GSMA).

At the Mobile World Congress conference, which is taking place in Barcelona this week, the GSMA revealed that it intended to provide the data to advertisers, in a bid to improve the advertising market of the mobile web.

Chief marketing officer, Michael O'Hara told The Guardian: "We can see the top sites, see where people are browsing regularly. See the time that sites are being viewed, the number of visits, the duration of visits and we can also get demographic data so you can have age ranges, male/female ranges".

"You can really start to build up a compelling case that says if you are a media company or advertising company, this is where you should be targeting your spending."

In a bid to quash privacy fears, the GSMA said that the data in its trial, which used deep packet inspection technology to collect data on users of the five main UK mobile networks; 3, O2, Orange, T-Mobile and Vodafone, had been 'anonymised'.

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"The demographic information is not picked up from your profile with the mobile operator. It is based on an opt-in, with people filling out a profile as a text message or with a link to a web page. When you fill that profile in, it links that information across to the activity."

Controversial online targeted advertising system Phorm, which has recently been trialled by ISP BT, makes the same claims, but this has done nothing to prevent privacy concerns being raised by a number of bodies, including the European Commission.

The GSMA's trial revealed that 68 percent of handset users surf the mobile web and the most popular website was Google. Social networking is also popular with mobile web users. On average mobile phone users visited Facebook an average of 3.3 times a day, clocking up 24 minutes per day on the site.

"We are moving to commercial launch of publishing a set of metrics on a regular basis," he said. "At the moment, if you were trying to buy space in mobile you would essentially use survey data, so this is a major step forward."

See also: Opera Turbo speeds up mobile web browsing