“Cookies: expiring sooner to improve privacy” Google announced overnight, referring to the data files it downloads on to its users' computers when they visit one of its sites.

To explain: cookies are used to “remember” your online preferences – for example the language you speak – when you revisit a site and help companies build up a profile of you. In a twist, so-called “third-party cookies” can be used to track your progress across several sites – valuable information for advertisers, but data that could be perceived as intrusive.

Most browsers allow users to block cookies, but they help the web work more smoothly and many sites are rendered inaccessible if you do not allow them on to your computer.

Nevertheless, they have long been a target for privacy campaigners. Google’s, in particular, have long been criticised for their longevity – they did not expire until 2038. The group was hoping to earn brownie points by cutting that span down to two years.

Google's privacy credentials are key to its commercial ambitions.

In May, Eric Schmidt, the Google chief executive, said that the company did not yet “know enough about you” and was stepping up its efforts to collect personal information on the web. “This is the most important aspect of Google's expansion,” he said.

There is, however, plenty of potential resistance to those plans.

The Article 29 working group – made up of national European Union data watchdogs, including the UK’s Information Commissioner’s Office – wrote to Google this year asking it to justify keeping logs of internet searches that can be used to identify individual users for two years.

The company responded by cutting the length of time that it stores that information to 18 months.

Meanwhile, competitors including WPP, the advertising group, and Microsoft, the software giant, have complained over the way in which Google's $3.1 billion acquisition of DoubleClick, the largest broker of online banner advertising, will make it privy to a vast amount of data on consumers' habits and companies' spending.

Amid these concerns, will the cookie step-down make a difference?

Google’s willingness to revisit policy on a totem issue has been welcomed. But, actually, as countless bloggers rushed to point out, the move will make little difference to Google users’ privacy, because cookies will be refreshed each time they visit a Google site.

Meanwhile, on the topic of transparency, Google was unable this morning to confirm immediately just how many types of cookies it uses (a statement mentioned one, but some browsers will allow a single web domain to download up to 50 on to your PC).

Also, it could not say immediately whether the cookies used on Google.com extend to YouTube.com, its video-sharing site.

"We're still working on that," a spokesman said.

Critical bloggers demand quick answers on sensitive topics. Google’s cookie monster is not dead yet.

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