Microsoft has chipped in with its own claim to internet search privacy protection by announcing it will make all records of search queries anonymous after 18 months.

The software company also called on others within the internet search industry to adopt a set of privacy principles, which would regulate the use of personal information for the purposes of search advertising.

Google, the leader in internet search, said in March that it would limit the period it kept personal information relating to search queries to 18 months, and last week said its 'cookies' — the files a website stores in a user's computer so it can be identified the next time it visits — would expire after 2 years.

In a separate development, Yahoo said that it would make its search data anonymous after 13 months unless a user requested otherwise.

Microsoft's announcement reflects the growing concern among search companies to respond to users' worries about privacy whilst at the same time harvesting the information they collect to improve their service.

The firm also said that it would now allow users to opt out of receiving ads based on their previous use of the internet; 'behaviourally targeted ads' are a feature of Microsoft's Windows Live — as well as Yahoo and AOL — searches, but are not currently offered by Google.

In a statement today Microsoft refused to say how long it kept search data for at present, but said the policy to make such information anonymous after 18 months "will be applied retroactively."

Peter Cullen, the chief privacy strategist at Microsoft, said that there should be a uniform approach among search engines to the way they use personal information. "We hope others will join us in developing principles that address these important issues. People should be able to search and surf online without having to navigate a complicated patchwork of privacy policies," he said.

Ask.com, which is fourth in internet search in the UK, has said that it is developing a product called Ask Eraser, which would store no information about a user's search at all.

According to comScore, Google was responsible for 76.6 per cent of searches conducted in the UK in May; Yahoo was second with 8.3 per cent, followed by Microsoft's Windows Live search (6.7 per cent) and Ask.com (3.8 per cent).