Google will try to cleanse identifying information from its search data, a major policy change around the contentious issue of how Internet companies treat data on people's online activity.

Google will "anonymize" server logs after 18 to 24 months by changing some of the digits in logged IP addresses and altering cookie file information. Google describes it as a balance between having data to improve service and being open about the data it retains.

The security of search data is a controversial issue. AOL got in trouble last year when it posted search data for academic researchers to use that it thought was anonymous. It turned out the data could be tracked to individuals. Google in 2005 fought a Justice Department subpoena in 2005 demanding search data, a request AOL, Microsoft, and Yahoo complied with. A court granted the Justice Department only a small portion of the URLs it sought from Google.

Federal officials have urged Internet companies to retain server log data for at least two years to help law enforcement. The industry has resisted, skeptical that such data would be valuable enough to justify the cost. For example, it doesn't take a high level of tech sophistication to avoid being identified by an IP address, says David McClure, CEO of the U.S. Internet Industry Association.

With its change, Google doesn't guarantee anonymity, only that it's highly unlikely a user could be identified. It's also highly unlikely that we've seen the end of the debate around search data.