MENLO PARK: 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 has gradually rolled out in the past month without disclosing the modifications. 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. Any reshuffling of Google's search rankings can have sweeping ramifications because they steer so much of the internet's traffic. Google fields about two of out every three search requests in the US 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.