Furthermore, we learn that a single data source is typically not sufficient to validate an incident and that multiple sources should be combined. In more than 10% of the cases, no single source, but the overall behavior of a host as seen from multiple sources helped to validate an infection. In addition, multiple sensors are needed in 70.5% of all cases when the easier to detect spyware are excluded. These results highlight the importance of a holistic approach in security assessment that combines multiple data sources. In order to detect elaborate pieces of malware, as the ones shown in Table 3, we need to combine local information about the exposure level and the behavioral patterns of studied hosts with public knowledge about the maliciousness of contacted domains. In this context, future work could also use a variety of tools to complement some of the sensors used in our study. For example, security inspectors (e.g., SecuniaPSI, QualysGuard), IDSs (e.g., BRO, Surricata), and NetFlow anomaly detectors can also be used to detect malicious activity, whereas spamtraps, blocklists, and DNS-based reputation engines can be exploited to build profiles of contacted domains.