Software updates are designed to improve security, add new features, and generally improve hardware. Sometimes, however, the effect is the opposite of what was intended, and so was the case for Macs, where the update disabled the Ethernet port.
After installing the latest update for OS X, Mac users were surprised to see that their hardware stopped working on the Ethernet port, causing many users to be cut off from the web and forced to switch to wireless.
This is certainly a very cumbersome fault, especially for people using internet accessories that do not offer wireless connectivity, but fortunately Apple has already dealt with this matter. The company representatives confirmed that they knew the problem and had already provided a fix that would eliminate it.
Installing the update requires a few steps, but it should not be a particularly difficult process, as Apple has provided a thorough tutorial explaining step by step what to do (-us / HT6672).