Introduction

sniff (snif)

v. sniffed, sniff ing, sniffs.

v. intr.

1. a. To inhale a short, audible breath through the nose, as in smelling something.

   b. To sniffle.

2. To use the sense of smell, as in savoring or investigating: sniffed at the jar to see what it held.

3. To regard something in a contemptuous or dismissive manner: The critics sniffed at the adaptation of the novel to film.

4. Informal. To pry; snoop: The reporters came sniffing around for more details.

As these definitions describe, the word sniffing has a number of meanings. Although we believe that hackers generate irritating sniffling noises, sniff at jars to determine their contents, and especially sniff in contempt, we really are interested in the last meaning: the process of prying or snooping.

What Is Sniffing?

Sniffing is method by which an attacker can compromise the security of a network in a passive fashion. A sniffer, in network security circles, is a program or tool that passively monitors a computer network for key information that the attacker is interested in. In most cases, this information is authentication information, such as usernames and passwords, which can be used to gain access to a system or resource. Sniffers are included with most rootkits. If your UNIX machine has been broken into, it is likely running a sniffer right now.