As discussed in “Google Hacking for Penetration Testers
If an attacker is willing to throw tons of packets at a target network, he can develop a fairly decent list of targets in very short order. In most cases the quality of the target list often depends on the sheer volume of traffic and the amount of time and effort the attacker is willing to expend on the exercise.

The link for this article located at InfoSec Writers is no longer available.