1. Method for adapting security policies of an information system infrastructure in function of attacks comprising the steps of: storing potential attacks and their associated risks in a data repository implemented in a hardware storage device; storing curative security policies in response of the potential attacks in a data repository said method further comprising the steps, implemented in a hardware processing means, of; monitoring entering contents representing data streams of the information system; detecting at least one attack in the information system; assessing a success probability parameter of the at least one detected attack and its associated cumulative cost impact parameter, further comprising the steps of generating attack strategy graphs based on the stored potential attacks and the detected at least one attack; and assessing the probability for the detected attack to reach its objective; assessing an activation impact parameter of at least one curative security policy in response to the at least one detected attack and its associated cumulative cost impact parameter; deciding of the activation or deactivation of a curative security policy in function of the success probability parameter of the, at least one, detected attack, of the activation impact parameter of at least one curative security policy and of the cumulative cost impact parameters of both the detected at least one attack and the at least one curative security policy.