For many of its users, Google offers Web search results that are customized based on their previous search history and clicks. For example, if someone consistently favors a particular sports site, Google will put that site high in the results when they look up sports topics in its search engine.

But there has always been one catch: people had to be signed in to a Google account to see such customization.

On Friday Google said it was extending these personalized search results to people who are not logged into the service.

The new service, according to a Google blog post, will use an anonymous cookie on a user’s computer to customize search results based on the user’s last 180 days of search activity. A “view customizations” link will appear on the top right of the search results page, and will lead to an explanation of how the results have been tailored and how the feature can be turned off.

“Our goal is to provide relevant search results,” said Nathan Tyler, a Google spokesman. “The benefits that we’ve seen for signed-in users were so great we want to extend those same benefits to everyone.”

But the change is already irking privacy advocates, who say that using Google while not logging in was one way to minimize exposure to its data-collection practices.

“The key point is that Google is now tracking users of search who have specifically chosen not to log in to a Google account,” said Marc Rotenberg, executive director of the Electronic Privacy Information Center in Washington. “They are obliterating one of the few remaining privacy safeguards for Google services.”

In an evaluation of the announcement on the blog Search Engine Land, Danny Sullivan noted that there was no way for searchers or others to view the saved search records on Google, and that Google was giving people the opportunity to permanently opt out of the arrangement.

“All the major search engines have long recorded what you search on. Google’s simply using it to refine your results,” Mr. Sullivan wrote.