When asked to disclose personal information to web questionnaires users may choose between various strategies of non-disclosure. An active strategy results in choosing an option like "I don't want to say", if available. Following a passive strategy means leaving the default option (e.g. "Please choose answer here") untouched. Being motivated to use active and passive non-disclosure strategies is assumed to depend on the sensitivity of the questions asked. In the present paper, in three experiments with several thousand participants we investigate how the sensitivity of questions and the design of answer options combine to influence non-disclosure to web-based forms. Type of default selection and location turned out to be of major influence on (non-)response rates to sensitive items. Depending on condition, percentages of participants who non-disclosed ranged from 0 to 34.9%. Despite the large range in non-disclosure, no bias in answers was observed.