A suggestion by Microsoft that search engines in Europe should keep customer data for just six months before converting it to an anonymous format has caused consternation among other technology companies that claim this could prevent innovation and even threaten network security.

Microsoft, which represents 2 per cent of the European search engine market, keeps customer information for 18 months, while Google retains data for nine months and Yahoo for 13 months. Microsoft moved to change its position – on the condition other search engines did the same – following European Union proposals this year that six months was a more reasonable period.