Mobile botnets are an emerging security threat that aims at exploiting the wide penetration of mobile devices and systems and their vulnerabilities in the same spirit of traditional botnets. Mobile botmasters take advantage of infected mobile devices and issue command and control operations on them to extract personal information, cause denial of service or gain financially. To date, research on countering such attacks or studying their effects has been conducted in a sporadic manner that hinders the repetition of experiments and thus limits their validity. We present here our work on a hybrid experimental platform for mobile botnets that supports the execution and monitoring of related scenarios concerning their infection, attack vectors, propagation, etc. The platform is based on principles of flexibility, extensibility and facilitates the setup of scalable experiments utilising both real and emulated mobile systems. We also discuss a novel method of estimating the active bot population in a botnet and illustrate its deployment on the experimental platform.