This doctoral thesis consists of five research papers that address four tangential topics, all of which are relevant for the challenges we are facing in our socio-technical society: information, security, privacy, and anonymity. All topics are approached by similar methods, i.e. with a concern about conceptual and definitional issues. In Paper I—concerning the concept of information and a semantic conception thereof—it is argued that the veridicality thesis is false. In Paper II—concerning information security—it is argued that the current leading definitions (...) suffer from counter-examples, and lack an appropriate conceptual sense. Based on this criticism a new kind of definition is proposed and defended. In Paper III—concerning control definitions of privacy—it is argued that any sensible control-definition of privacy must properly recognize the context as part of the defining criteria. In Paper IV—concerning the concept of privacy—it is argued that privacy is a normative concept and that it is constituted by our social relations. Final, in Paper V—concerning anonymity—it is argued that the threat from deanonymization technology goes beyond harm to anonymity. It is argued that a person who never is deanonymized can still be harmed and what is at stake is an ability to be anonymous. (shrink)