A combination of shim and back-end server applications may be used to identify and block the installation of malicious applications on mobile devices. In practice, a shim application registers with a mobile device's operating system to intercept application installation operations. Upon intercepting an attempted installation operation, the shim application identifies the application seeking to be installed, generates a key uniquely identifying the application, and transmits the key over a network connection to a back-end server. The back-end server may be configured to crawl the Internet to identify malicious applications and compile and maintain a database of such applications. Upon receiving a key from the shim application, the back-end server can search its database to locate a matching application and, if found, respond to the mobile device with the application's status (e.g., malicious or not). The shim application can utilize this information to allow or block installation of the application.