Even though purely text-based Human Interaction Proofs (HIPS) have desirable usability and accessibility attributes; they could not overcome the security problems yet. Given the fact that fully automated techniques to generate pure-text HIPs securely do not exist, we propose leveraging human computation for this purpose. We design and implement a system called SMARTCHA, which involves a security engine to perform automated proactive checks on the security of human-generated HIPs and a module for combining human computation with automation to increase the number of HIP questions. In our work, we employ HIP operators who generate around 22 000 questions in total for SMARTCHA system. With a user study of 372 participants, we evaluate the usability of SMARTCHA system and observe that users find solving pure-text HIPs of SMARTCHA system significantly more enjoyable than solving reCAPTCHA visual HIPs. (C) 2016 Elsevier Ltd. All rights reserved.