Driven from its self-styled caliphate in Iraq and Syria, Islamic State is down but not out. Where once they confronted armies, the extremist Islamist group's adherents have now staged hit-and-run raids and suicide attacks. In some cases, the group has claimed responsibility for atrocities, including the bombings of churches and hotels in Sri Lanka that killed at least 253 people. Its involvement is not always proven, but even if the link is ideological rather than operational, Islamic State still poses a security threat in many countries.