As the Internet becomes more pervasive in all areas of human activity, attackers can use the anonymity of cyberspace to commit crimes and compromise the IT infrastructure. As currently there is no generally implemented authentification technology we have to monitor the content and relations of messages and Internet traffic to detect infringements. In this paper, we present recent research on Internet threats such as fraud or hampering critical information infrastructure. One approach concentrates on the rapid detection of phishing email, designed to make it next to impossible for attackers to obtain financial resources or commit identity theft in this way. Then we address how another type of Internet fraud, the violation of the rights of trademark owners by the selling of faked merchandise, can be semi-automatically solved with text mining methods. Thirdly, we report on two projects that are designed to prevent fraud in business processes in public administration, namely in the healthcare sector and in customs administration. Finally, we focus on the issue of critical infrastructures, and describe our approach towards protecting them using a specific middleware architecture.