In an example there is provided a method for receiving notification of an intrusion event in relation to an application from an intrusion detection system, accessing state data in relation to a state of the application prior to the intrusion event, the state data having been stored on the basis of a change of state of the application, accessing a policy to be applied to the state data in response to the intrusion event, modifying the state data on the basis of the policy, and restoring the application on the basis of the modified state data.