This thesis encapsulates research on the detection of botnets. First, we design and implement Sandnet, an observation and monitoring infrastructure to study the botnet phenomenon. Using Sandnet, we evaluate detection approaches based on traffic analysis and rogue visual monetization. Therefore, we identify and recognize botnet C&C channels by help of traffic analysis. To a large degree, our clustering and classification leverage the sequence of message lengths per flow. As a result, our implementation, CoCoSpot, proves to reliably detect active C&C communication of a variety of botnet families, even in face of fully encrypted C&C messages. Furthermore, we found a botnet that uses DNS as carrier protocol for its command and control channel. By help of statistical entropy as well as behavioral features, we design and implement a classifier that detects DNS-based C&C, even in mixed network traffic of benign users. Finally, perceptual clustering of Sandnet screenshots enables us to group malware into rogue visual monetization campaigns and study their monetization properties
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