for scanners/indexes of public services your might search for "shodan"

for the valid use of security trhough obscurity:

"My thoughts on this are that obscuring information is helpful to security in many cases as it can force an attacker to generate more "noise" which can be detected.

Where obscurity is a "bad thing" can be where the defender is relying on that obscurity as a critical control, and without that obscurity, the control fails.

So in addition to the one you gave above. An effective use of obscurity could be removing software name and version information from Internet facing services."

src: Rоry McCune / http://security.stackexchange.com/questions/2430/the-valid-role-of-obscurity