Software testing in the cloud can reduce the need for hardware and software resources and offer a flexible and efficient alternative to the traditional software testing process. A major obstacle to the wider use of testing in the cloud is related to security issues. This chapter focuses on test generation techniques that combine concrete and symbolic execution of the program under test. Their deployment in the cloud leads to complex technical and security issues that do not occur for other testing methods. This chapter describes recent online deployment of such a technique implemented by the PathCrawler test generation tool for C programs, where the author faced, studied, and solved many of these issues. Mixed concrete/symbolic testing techniques not only constitute a challenging target for deployment in the cloud, but they also provide a promising way to improve the reliability of cloud environments. The author argues that these techniques can be efficiently used to help to create trustworthy cloud environments.