Live monitoring of Internet content is now providing new possibilities for early warning of security threats across a range of fields. This paper reviews the techniques available, their methodologies, and their application to three areas. The first is regional conflict early warming. The second is terrorism forecasting and early warning. The third area is disease outbreaks and health threat monitoring. The main challenges in this research are information retrieval in multiple languages, extraction of relevant data and information from unstructured text, the development of methodologies and indicators capable of detecting trends and small trigger signals. For such early warning systems to be effective they must inform operators of potential threats without an undue number of false alarms. This paper reviews the techniques used for information retrieval and extraction, and describes three applications in the areas concerned.