Sanctions require international agreement to be effective  When is it legitimate to use sanctions in response to an action? Any individual state (or group of states) can use sanctions against any other state. However for these sanctions to be effective they need to have broad based support. Sanctions by an individual country are unlikely to change the behaviour of an aggressor as they will be able to get around the sanctions. Moreover for any country that is a member of the WTO imposing sanctions may be considered illegal allowing the other country to counter them with similar measures.  The problem then is that there is no international response to hacking and it is unlikely there will be agreement on such a response. When countries like China deny that hacking comes from them are they likely to support the use of sanctions against such actions? Sanctions for much worse actions are often bogged down when they are attempted at the international level such as China and Russia vetoing sanctions against Syria in response to the violence there. [1]  [1] United Nations Security Council, ‘Security Council fails to adopt draft resolution on Syria that would have threatened sanctions, due to negative votes of China, Russian Federation’, un.org, SC/10714, 19 July 2012,