Web search engines (WSEs) collect and store information about their users in order to tailor their services better to their users’ needs. Nevertheless, while receiving a personalized attention, users lose control over their own data. Search logs can disclose sensitive information and the real identities of users, thus creating serious risks of privacy breaches. Privacy preserving techniques seek to limit these risks by modifying the data. Although privacy is preserved, the data utility is reduced in a consequence of the data modifications. Achieving a good trade-off between privacy and utility can be a difficult task. In the present thesis we discuss the problem of limiting privacy disclosure risks in search logs while preserving enough data utility. The first part of this thesis focuses on the methods to prevent the gathering of information by WSEs. Since search logs are convenient in order to receive an accurate service, the aim is to provide logs that are still suitable to provide personalization. To that end, we propose a protocol which uses a social network in order to hide the queries submitted by a user. Results shows that users achieve good levels of privacy, meanwhile the response time of the protocol is acceptable.
