Yes, with a caveat: permission must be granted beforehand, explicit or implicit. Explicit permission is easy enough; implicit permission gets into a murky area not yet fully codified in US law. Thus the various judgments of various courts.

It's always best to be clear beforehand. Law officers are fond of stating "ignorance is no excuse".

EDIT: oh, and in the US "damage" has already been construed in some cases to include degradation of service performance...