Packet sniffers or protocol analyzers are tools used by network engineers to diagnose network-related problems. Hackers use packet sniffers for less noble purposes, such as spying on network user traffic and collecting passwords.

Packet sniffers come in a variety of forms. Some packet sniffers used by network engineers are single-purpose hardware solutions. Other packet sniffers, on the other hand, are software applications that run on standard consumer computers and use the networking hardware provided on the host device to perform packet capture and injection tasks.

Packet sniffers work by intercepting and logging network traffic through the wired or wireless network interface on the host computer.

On a wired network, the information that can be captured depends on the structure of the network. A packet sniffer may be able to see traffic on an entire network or just a specific segment; it depends on how the network switches are configured. On wireless networks, packet sniffers typically capture one channel at a time, unless the host computer has multiple wireless interfaces that allow multichannel capture.