The security of application installers is often overlooked, but the security risks associated to these pieces of code are not negligible. Online public repositories have been one of the most popular ways for end users to obtain software, but there is a lack of systematic security evaluation of popular public repositories. In this paper, we bridge this gap by analyzing five popular software repositories. We focus on their software updating dynamics, as well as the presence of traces of vulnerable and/or trojanized applications among the top-100 most downloaded Windows programs on each of the evaluated repositories. We analyzed 2,935 unique programs collected in a period of 144 consecutive days. Our results show that: (i) the repositories frequently exhibit rank changes due to applications fast climbing toward the first positions; (ⅱ) the repositories often update their payloads, which may cause the distribution of distinct binaries for the same intended application (binaries for the same applications may also be different in each repository); (ⅲ) the installers are composed by multiple components and often download payloads from the Internet to complete their installation steps, posing new risks for users (we demonstrate that some installers are vulnerable to content tampering through man-in-the-middle attacks); (ⅳ) the ever-changing nature of repositories and installers makes them prone to abuse, as we observed that 30% of all applications were reported malicious by at least one AV.
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