Microsoft this week revealed plans to limit retention of Internet search data in Europe to six months, but said it would follow through on the offer only if other search companies, most notably Google, follow in step.

"We don't believe that Microsoft moving alone will offer the level of consumer protection desired," wrote Microsoft chief privacy strategist Peter Cullen, in a blog post.

While that might sound like so much corporate buck-passing, Cullen has a point -- and not for reasons Microsoft is likely to brag about. That fact is, the European search market is even more dominated by Google than the U.S. market.

Google sites control about 80% of the market in Europe, compared to Microsoft's puny 2% stake. Even if Microsoft acquires Yahoo's search operations, a scenario that's becoming increasingly likely, its share would rise only to 4%. Clearly, Microsoft acting alone on search privacy initiatives would do little to assuage Internet users' fears that corporate marketers are tracking their every click.

For its part, Google has yet to state whether it plans to adopt guidelines similar to what Microsoft is proposing.

Microsoft's proposal came in response to a European Commission recommendation that Internet search providers "anonymize" user data after six months in order to protect privacy. Currently, most providers maintain such data for more than a year.

Cullen concedes that concerns are not unwarranted: "There have been documented instances of when search queries can be linked across sessions and over time, some individual users can possibly be identified, even in the absence of a full or partial" Internet address.

"Consumers want assurance that their privacy is protected while also being provided with search and other online services that meet their needs," wrote Cullen.