El Capitan's System Integrity Protection
 

With El Capitan released, there's one 'feature' that really needs to be highlighted - for better or worse. System Integrity Protection (SIP, sometimes referred to as rootless) is a security feature of OS X El Capitan, the operating system by Apple Inc. It protects certain system processes, files and folders from being modified or tampered with by other processes even when executed by the root user or by a user with root privileges (sudo). Apple says that the root user can be a significant risk factor to the system's security, especially on systems with a single user account on which that user is also the administrator. System Integrity Protection is enabled by default, but can be disabled. Here's Apple's WWDC presentation about SIP.

http://osnews.com/story/28877/El_Cap...ity_Protection