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Implicit user feedback is known to be a strong signal of user preferences in web search. Hence, solving the explorationexploitation dilemma [5] became an important direction of improvement of ranking algorithms in the last years. In this poster, in the case of commercial queries, we consider a new negative effect of exploration on the user utility-distracting and confusing users by shifting well-known documents from their common positions-and propose an approach to take it into account within Multi-Armed Bandit algorithms, usually applied to solve the dilemma.

The paper describes the experience of resisting the large-scale solving of CAPTCHA through the CAPTCHA-farms and presents the results of experimenting with different types of textual CAPTCHA on the farm worker and casual user crowds. Localization of CAPTCHA led to cutting twice the absolute volume of CAPTCHA parsing, but introducing the semantics into the test complicated it to casual users and was not found promising.