Police forces across Europe have discovered dozens of bomb manuals for creating chemical weapons. Special counter-terrorism units from 17 countries worked together with Europol’s European Counter Terrorism Centre to restrict access to instructions online on how to use high-risk chemicals for terrorist attacks. Investigators scoured the web to identify and refer for removal, propaganda and instructions on the use of high-risk chemicals, and the toxic gases they generate, in terrorist material. A number of chemicals routinely used in industrial processes or professional functions can react upon mixing, producing hazardous substances that could be used to carry out chemical terrorist attacks. The investigation resulted in more than 120 instances of content being referred to 21 online service providers to ensure their swift removal. The referred content covered five languages and was disseminated by terrorist-supporting networks, including Islamist, right-wing and left-wing terrorist groups. Participating countries included Denmark, France, Germany and the United Kingdom.