Software engineering practices strongly affect the security of the code produced. The increasingly popular Rapid Release Cycle (RRC) development methodology and easy network software distribution have enabled rapid feature introduction. RRC's defining characteristic of frequent software revisions would seem to conflict with traditional software engineering wisdom regarding code maturity, reliability and reuse, as well as security. Our investigation of the consequences of rapid release comprises a quantitative, data-driven study of the impact of rapid-release methodology on the security of the Mozilla Firefox browser. We correlate reported vulnerabilities in multiple rapid release versions of Firefox code against those in corresponding extended release versions of the same system; using a common software base with different release cycles eliminates many causes other than RRC for the observables. Surprisingly, the resulting data show that Firefox RRC does not result in higher vulnerability rates and, further, that it is exactly the unfamiliar, newly released software (the "moving targets") that requires time to exploit. These provocative results suggest that a rethinking of the consequences of software engineering practices for security may be warranted.