In squashing software bugs, you inevitably introduce new ones—that's a fact of life. According to a thread on Reddit, Apple's recent OS X security update has inadvertently disabled the Ethernet port for some owners of Apple's all-in-one desktop and the MacBook Pro notebook.
Making matter worse is the fact that Apple pushed this security update via the silent updating mechanism, according to a poster on Reddit who probably enabled the option in System Preferences → App Store that prompts OS X to automatically install system data files and security updates.