An Advanced Persistent Threat (APT) is a cyber attack directed at businesses or political targets. It is usually launched by a group, such as a government, with both the means and the intent to persistently target a specific entity. The effort involved is usually very large to make the attack successful, to remain undetected and to ensure continued control. An example for an APT is the Stuxnet worm which was targeted at Iran’s nuclear centrifuges.