The separation between a physical, “real” world and a digital, “virtual” world is vanishing. Computer systems control physical infrastructure and, contrariwise, the often adjured cyber world relies on physical cables, switches, and other hardware. This level of interdependency accounts for a great vulnerability to terrorists who want to generate fear, destroy property and human lives, or harm the economy. However, apart from attacks that are committed via the Internet, it is also used to disseminate terrorist content. Ultimately, conventional uses, e.g. worldwide individual communication or access to formerly unavailable or hard-to-obtain information are an advantage for terrorists. This chapter analyzes these possible forms of use of the Internet by terrorists and gives examples of cases and threats that have either already occurred in the past or are likely to occur in the future.