Actually google updates their algorithm in certain interval of time. and this update is done to ban spammers. each and every time google names their updates,, like - panda, penguin and now came the humming bird. even though the impact of humming bird is not fully realized, they are in active. some says this update if focused on keywords and this opinion varies between experts. all you need to do to escape from this update is - prefer white hat seo,, good contents with quality links and regular updates will guide you in a better way