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Google has overhauled the way it serves up results in response to search queries.

The update is designed to work out whether a person wants up-to-date results or historical data.

The US firm estimated the alterations to its core algorithm would make a difference to about 35% of searches.

The changes try to make results more relevant and beef up features which Google believes set it apart from rivals.

By contrast, Microsoft's Bing search engine emphasises social search.

Fresh spam

"Search results, like warm cookies right out of the oven or cool refreshing fruit on a hot summer's day, are best when they're fresh," wrote Google fellow Amit Singhal in a .

The under-the-hood changes sought to understand whether a searcher wants results "from the last week, day or even minute" said Mr Singhal.

The update is supposed to offer a better guess of how "fresh" the results should be.

For instance, said Mr Singhal, anyone searching for information about the "Occupy Oakland protests" would probably want up to the minute news.

These need to be distinguished from searches for regular events such as sports results or company reports.

Other types of searches could call on older results, he said. Those looking for a recipe to make tomato sauce for pasta quickly would be happy with a page that is a few months or years old.

The update to improve the "freshness" of results builds on the big update made to the underlying infrastructure of Google's core indexing system in August 2010 known as Caffeine. That change made it easier for Google to keep its index up to date and to add new sources of information.

Writing on the . The last big update to the Google algorithm, known as Panda, affected only 12% of searches.

The update could have potential disadvantages, warned Mr Sullivan.

"Rewarding freshness potentially introduces huge decreases in relevancy, new avenues for spamming or getting "light" content in," said Mr Sullivan.