Google has quietly retooled the closely guarded formula running its Internet search engine to give better answers to the increasingly complex questions posed by Web surfers.

The overhaul came as part of an update called “Hummingbird” that Google Inc. has gradually rolled out in the past month without disclosing the modifications.

Google disclosed the existence of the new search formula on Thursday, its 15th birthday, at an event held in Menlo Park, California, garage. Its birthday is celebrated on September 27, even though the company was incorporated a few weeks earlier.

The changes could have a major impact on traffic to websites. Hummingbird represents the most dramatic alteration to Google’s search engine since it revised the way it indexes websites three years ago as part of a redesign called “Caffeine,” according to Amit Singhal, a senior vice-president for the company. He estimates that the redesign will affect the analysis of about 90 per cent of the search requests that Google gets.

Google fields about two of out every three search requests in the U.S. and handles an even larger volume in some parts of Europe. The changes could also drive up the price of Google ads tied to search requests if websites whose rankings are demoted under the new system feel they have to buy the marketing messages to attract traffic.

The change needed to be done, Mr. Singhal said, because people have become so reliant on Google that they now routinely enter lengthy questions into the search box. Besides Hummingbird, Google also announced a few other updates, primarily affecting “Knowledge Graph” and Google Now, a virtual assistant.

Besides providing snapshots of famous people and landmarks, the Knowledge Graph is now capable of comparing the attributes of two different things, such as olive oil and coconut oil.

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