Lone-wolf terrorism is a threat to the security of modern society, as was tragically shown in Norway on July 22, 2011, when Anders Behring Breivik carried out two terrorist attacks that resulted in a total of 77 deaths. Since lone wolves are acting on their own, information about them cannot be collected using traditional police methods such as infiltration or wiretapping. One way to attempt to discover them before it is too late is to search for various ‘‘weak signals’’ on the Internet, such as digital traces left in extremist web forums. With the right tools and techniques, such traces can be collected and analyzed. In this work, we focus on tools and techniques that can be used to detect weak signals in the form of linguistic markers for potential lone wolf terrorism.