Someone Else's Problem Fields
In an ideal world, a simple machine called a "Someone Else's Problem Field Generator" would exist. This device would produce a field which can be erected on, or projected around a network and all hosts contained within so that the unconscious minds of the observers instantly abdicate responsibility for its existence, assert that it's "somebody else's problem", and therefore don't perceive it at all.
Someone Else's Problem fields are much more efficient than an invisibility field due to the natural propensity of humans to see things as Somebody Else's Problem. In fact, studies have proven that a single flashlight battery can run it for over a hundred years.
Unfortunately, such a device does not exist. This is not a bad thing, for if it did exist, it would be virtually useless because for the malicious user, your network is their problem, and as a result, they would be able to see it.
If you wish to impliment something similar to a "Someone Else's Problem Field Generator", you may wish to impliment the "Security Through Obscurity " model of computer security.
Works Cited: Life, the Universe and Everything Douglas Adams