Organizations that provide centralized security monitoring of the networks of multiple third-party organizations are faced with a challenging task. The amount of security event data to be processed presents not only a technical challenge, but also a problem-solving challenge to operators. We present a model of the problem-solving process and discuss how visual support tools can facilitate the central problem-solving step called new event triage. We argue that with tools such as these the natural benefits of centralized monitoring can come into play, which enhances effectiveness of centralized monitoring to a level beyond the reach of organizations focusing exclusively on their own network.