Physical access to network wires needs to be protected. Unfortunately, the vast amount of wire inherent in most LANs provides many points for unauthorized access. Often, if users from inside can get out to the Internet, then users from outside can get into a network if proper precautions haven't been taken. Many products are available to help network administrators secure their networks from the above threats. User authentication and authorization is provided by most network operating systems, and can be enhanced by adding third-party products.
Wired networks are particularly vulnerable to eavesdropping.
Inexpensive and readily available programs let anyone with physical access to the network to read, capture, and display any type of packet data on the net. And even wired LANs have an unintended wireless component. Many types of LAN cabling, particularly unshielded twisted pair, radiate significant energy. This leads to the possibility that anyone with a strong motivation, the right radio equipment, and a good antenna can sit in the parking lot outside a building and actually intercept wired Ethernet data packets - without detection. Data encryption is the only line of defense against this kind of threat.