Nov. 6 (Bloomberg) — Google Inc., Microsoft Corp. and Yahoo! Inc. must limit the amount of time they keep Internet- search records after failing to justify keeping the information beyond six months, European Union officials probing possible breaches of EU privacy laws said.

“The Working Party is not convinced by the justifications put forward” by Google, Microsoft and Yahoo for the longer storage periods, the Article 29 Data Protection Working Party said in letters to the companies dated Oct. 23. The group said it “strongly recommends” the companies revise their retention period to six months or less.

The Article 29 group’s proposals guide the work of national authorities across Europe, which have the power to levy penalties for non-compliance. Shortening the time that search engines keep such records could eat into advertising revenue. The companies rely on users’ queries to target advertising more specifically.

The letters follow a meeting the companies had with the data-protection officials in February to question them on the reasons for longer storage periods. The data officials in a decision last year unanimously agreed that the three companies’ storage policies didn’t comply with European Union privacy laws.

‘Careful Balance’

“Protecting users’ privacy and providing them with the safe and useful search experience they expect is a careful balance that Google takes very seriously,” Peter Fleischer, Google’s global privacy counsel, said in an e-mailed statement. “The characteristics of the data that help prevent fraud and malware; correct users’ spelling mistakes; or provide Flu Trends, which could help prevent outbreak of illness, are the same characteristics that introduce privacy risks.”

Jesse Verstraete, a spokesman for Redmond, Washington-based Microsoft in Brussels, said the company had received the letter and is reviewing it.

“Under the policy, Yahoo will anonymize user log data after 90 days with limited exceptions to fight fraud, secure systems and meet legal obligations,” Nina Blackwell, a Yahoo spokeswoman, said in an e-mailed statement. “We are committed to protecting our users’ privacy and will continue to work with the Article 29 Working Party going forward.”

Yahoo signed an agreement with Microsoft in July to use Microsoft’s Bing search engine on its Web sites and sell ads that appear next to Web-search results, with the companies splitting the revenue.

Yahoo’s Commitments

While the data officials received confirmations from Yahoo that it would “live up to the commitments,” the group said it “still awaits details of how your policy will be implemented now that part of the search-related personal data are being processed by Microsoft.”

Mountain View, California-based Google has cut its data storage period to nine months from 18 months. Microsoft, which keeps data from its search engine for 18 months, said it would only shorten that period if others did too.

“There are still some issues which deserve further clarification,” the data officials, who represent the 27 EU nations, said in the letters. They gave the companies three months to reply.