In a move that could make it harder for its users to remain anonymous, Google said it would start combining nearly all the information it has on its users.

This could mean, for instance, that when users search via Google, the company will use their activities on sister sites like Gmail and YouTube to influence those users' search results. Google has not done that before.

Google's move -- which was disclosed in a privacy policy that will take effect on March 1 -- is a sign of the fierce competition between Google and Facebook over personal data. Facebook has amassed an unprecedented amount of data about the lives of its more than 800 million members -- information that is coveted by advertisers.

Google traditionally has not had the same amount of personal data about its users, and has kept much of its personal data separate. But as Facebook gears up for its planned initial public offering this spring, Google has amped up the competition.

Last year, Google launched its own social network, called Google+, and earlier this month Google started including data from Google+ in members' search results. Google's latest move would allow the company to include insights from services such as Gmail and YouTube to search results as well. This could effectively rewrite the relationship between users and the world's most-popular search engine.

Read more on Google's sweeping privacy changes at The Wall Street Journal.