European data protection officials are expanding their examination of the impact search engines have on privacy, after initially targeting Google last month, European data protection Supervisor Peter Hustinx said in an interview.

A panel of European data protection officials called the Article 29 Working Group decided to request information from Google's rivals amid concerns that search engines are holding onto information about the people who use them for too long, Hustinx said.

Hustinx, a senior member of the working group, declined to name the companies. However, they are believed to include Yahoo, Lycos and Microsoft's Windows Live.com.

The working group will make a general assessment of the state of European citizens' privacy in relation to search engines at its meeting in October or December 2007, he said.

"We will issue a generic paper from which national data protection authorities can address players in their jurisdictions," Hustinx said Google does present specific problems, he added, because so many of its services pose a possible threat to privacy. He mentioned Google Earth and Gmail, Google's Web-based e-mail service. Compiling information about people from the various different Web services could compound the threat to privacy, he said.

Google has already replied to the letter it received from the working group last month. "The use of the Internet the way Google is doing it could introduce tremendous privacy problems. We will study the company's response to our letter very carefully," Hustinx said. "If the picture they give is not accurate or not justified we might find ourselves on a collision course," he said, but he added: "That's not my sense at the moment." In Google's response, the company offered to shorten the time it keeps Web searches to 18 months from two years. The company also promised to look at shortening the lifespan of cookies it deposits on computers.

Google presently stores cookies, including ones that remember what language a person speaks, for 30 years.

Google's cooperation impressed Hustinx until now. "I welcome a big company that is investing in privacy. This isn't just window dressing," he said, echoing comments he made at a data protection conference in Amsterdam.

Broadening its examination beyond Google is an obvious next step, according to Danny Sullivan, who writes for searchengineland.com.

He compared the cookie policies of Google, Windows Live and Yahoo and found that Yahoo stores the data for as long as Google while Windows Live stores the information for 14 years.

However, Windows Live deposited far more cookies on computers than Google and Yahoo. Using a clean version of Windows Internet Explorer 7, Sullivan set it to reveal all cookies. Windows Live left 14 cookies as soon as he did a search; Yahoo left six, while Google left just two.

"Both Google and Yahoo have 30-year cookies. So where's the letter for Yahoo from the Working Group? And isn't 14 years from Microsoft excessive?" Sullivan wrote.

Yahoo and Microsoft both say they take privacy very seriously.

"Microsoft has a long-term commitment to providing customers with control over the collection, use and disclosure of their personal information. While we have not received formal communication from the Article 29 Working Party, we recognize that online search is creating legitimate concerns about privacy and are actively engaged with data protection authorities around the world to ensure that our practices meet the highest standards when it comes to protecting privacy," Microsoft said in a statement.

"Our users' trust is one of Yahoo's most valuable assets. That's why maintaining that trust and protecting our users' privacy is paramount to us. Our data retention practices vary according to the diverse nature of our services," Yahoo said.