But Google’s detailed personal profiles, which are created by harvesting the history of its account holders, isn’t always right.

Google’s 350m account holders have found themselves listed with the wrong age and the wrong sex, which casts doubt over the popular thinking Google knows more about what you like than your own partner.

This is because your age and gender are decided by those of other Google users who have visited the sites.

The profile page, called Ad Preferences, is hidden away inside a settings menu in Google Accounts.

The Ad preferences page came to light following a sweeping change to ‘privacy policy’, which comes into effect on March 1.

A debate about privacy policy flared up this week with the announcement the company would start tracking users across all of its sites, including YouTube.

Although you can opt out of the tracking, or manually edit your details, this sort of in-depth profiling raises, has privacy activists up in arms.

Rainey Reitman, activism director for privacy group Electronic Frontier Foundation, said with all their web use, consumers are leaving an “unfathomably large” data trail every day.

“There has never been another time in history where privacy was under the kind of assault it is today.”

YouTube data, Gmail information and search data will all be used to build up ever more accurate advertising profiles and also the company claims it will make searches more personalised.