Nmap, free open source utility for network exploration or security auditing, today counts for thirteen million lines of code representing four thousand years of programming effort. Hackers can use it to conduct illegal activities, and information security professionals can use it to safeguard their network. In this dual-use context, question of trust is raised. Can we trust programmers developing open source dual use security software? Motivated by this research question, we conducted interviews among hackers and information security professionals, and explored ohloh.net database. Our results show that contributors behind open source security software (OSSS) are hackers, OSSS have important dual-use dimension, information security professionals generally trust OSSS, and large organizations will avoid adopting and using OSSS.