It was Google that blinked first, in the wake of relentless criticism that search engines were piling up private data and information on the basis of the keywords we use in net searches.

Then, Ask.com joined the brigade. Now, in an effort to boost its privacy credentials, Microsoft has fallen into line with Google and Ask.com, as well as announced that it will allow web searchers to opt out of behaviourally targeted ads on its sites.

Behavioural targeting keeps track of the user''s habits as (s)he navigates through Microsoft''s network. It might send you ads for a sports store if it notices that you''re searching for a tennis racket.

Microsoft says it will store people''s search data for 18 months, after which it will ''anonymise'' that information. Till now, Microsoft, like other search engines, kept the data like the user''s IP address and search terms in its logs forever.

Microsoft''s proclamation comes only after similar privacy-restoring announcements from Google, Ask and Yahoo, which came after the US Federal Trade Commission and European regulators piled on the pressure. The search engines also sought to be one-up on each other in the war for privacy conscious users.

So which is the most private search engine? Read on:

Google: In March, Google said it would keep search logs for 18 months, after which it would make the data anonymous. Every time you use its search engine, Google keeps a note of your Internet address, your search query, and details from the ''cookies'' it places on your hard disk.

The company''s excuse for collecting the data is that it uses the search logs to run its spell checker, to track spam, fraud, and attacks on Google''s and other Internet machines. It also says that it has to comply with regulations and anti-terrorism laws.

It does not ''profile'' users for marketing. Google''s ad business is based on keywords, and you are served up an ad according to the keywords you type in a for a specific search. The site makes no attempt to determine your demographical profile (your sex, age, etc) based on your search history.

Microsoft: Microsoft Windows Live Search''s 18-month plan will be like Google''s, but Microsoft makes extensive use of demographic profiling. If you type ''compare TV prices'' on Live Search, Microsoft''s computer notes that you are interested in buying a TV set.

It then checks the list of Hotmail accounts to see if there is any information about you. If there is, and an electronics manufacturer has paid Microsoft to target people like you, the computer will automatically send a TV ad when you next look at a Microsoft web page.

Microsoft says that its tests in the US on behavioural targeting showed increased clicks on ads by as much as 76 per cent! Now, Microsoft''s new profiling policy says that users can opt out of demographic ad targeting.

Ask.com: It recently announced that in the near future, it would keep users'' search data for only 18 months. Bit it isn''t clear when Ask will do this. It wants to activate the new policy only when it launches a new feature called Ask Eraser, which will enable users to request that the company erase their search logs immediately.

But how Ask Eraser will work is a mystery. It is also not clear how Ask.com will circumvent the laws that Google says requires it to keep search data for at least 18 months.

Yahoo: A top company said in a newspaper interview that Yahoo will keep search-log data for only 13 months. That''s five months less than Google and Microsoft, but longer than Ask''s hypothetical immediate-deletion policy. Yahoo also does behavioural targeting, but has announced no plan to let people opt out of this practice.