1. A wiretap that eavesdrops on computer networks. Key point: You have be between the sender and the receiver in order to sniff traffic. This is easy in corporations using shared media, but practically impossible with an ISP unless you break into their building or be an employee. Key point: Sniffers are frequently used as part of automated programs to sift information off the wire, such as clear-text passwords, and sometimes password hashes (to be crack). Further reading: http://www.robertgraham.com/pubs/sniffing-faq.html. From Hacking-Lexicon