| Eavesdropping occurs when a hacker is able to see the information contained within a packet. One way of preventing eavesdropping is to encrypt the information that is being sent. Network layer encryption encodes the packet payload. A router or firewall encrypts and decrypts packets. A hacker with a packet sniffer can only see ciphertext in the packet payload. The IP and transport layers remain in clear text format, so the packet can find its way to the destination address.