Microsoft wrote in a blog post, "[Microsoft will] delete the entire Internet Protocol address associated with search queries at six months rather than at 18 months."
The Wall Street Journal reports that the change in how long Microsoft stores search data is in response to negotiations with European regulators. The move is expected to pressure search firms like Google to follow suit.
Microsoft hopes that by deleting user search quires more frequently it can lure users concerned about privacy to use Bing rather than Google. Google still claims that it needs to keep search queries stored for up to nine months to improve search quality and fight fraud. The fraud in question is termed click fraud and is when users or companies click on ads repeatedly to run up the advertisers bill with no intention of buying.
Yahoo stores IP addresses for 3 months, while Google keeps them for 9 months.
More info at DailyTech.