Apple's Gatekeeper security system in OS X allows you to limit running applications to those that are created by trusted developers. With this feature enabled, if you open an unsigned program directly instead of using the contextual menu, then you will get an error message and the program will not execute.
However, Gatekeeper also detects whether a program has potentially been altered, and will prevent such a program from running. This is an effort to prevent programs, signed or otherwise, from being tampered with by malware and hackers. When this happens, the system will issue a similar Gatekeeper warning … Read more