Have a clear escalation plan when trouble is suspected.
A major retailer had warnings there was trouble with a point of sale system, but the timing of the alerts coincided with critical shopping periods. The staff that were concerned did not have the authority to take the systems offline and investigate, nor could they locate anyone with the authority. Subsequently, a disaster ensued. The problem could have been contained had someone acted when they first suspected trouble. Be sure your staff knows who has the authority to make the hard call at the first sign of trouble or give them the authority to do so themselves.