A method of preventing a first action associated with a first message from being performed in a target entity, the method including the steps of: sending the first message to the target entity, the first message being configured to cause the entity to perform the first action and a second action; sending a second message to the target entity, the second message being configured to cause the entity to perform a third action; and wherein the entity is configured such that performance of the second action and the third action is mutually incompatible.