1. A method for providing computational integrity for a digital data processing system, comprising the computer-executed steps of: detecting, with a data processor, an anomalous behavior of a digital data processing system during program execution, the anomalous behavior being indicative of an undesirable informational state of the digital data processing system that may result from the presence of an undesirable software entity; scanning, with the data processor, one or more portions of an informational state history of the digital data processing system to detect, if present, at least one known type of undesirable software entity; in response to the detection of a known type of undesirable software entity, taking remedial action; else, if a known type of undesirable software entity is not detected by the step of scanning, detecting, with the data processor, a previously unknown type of undesirable software entity; extracting, with the data processor, an identifying signature from the detected undesirable software entity; storing the identifying signature so as to enable a future detection of the undesirable software entity as a known type of undesirable software entity; and taking remedial action; wherein the step of extracting includes the data processor executed steps of obtaining at least one sequence of bytes from the detected undesirable software entity, determining likelihoods that the at least one sequence of bytes is also found in program code that may be run on a digital data processing system which is to be protected from the undesirable software entity, and selecting as the extracted identifying signature a plurality of bytes from the at least one sequence that have a high likelihood of reliably identifying a future occurrence of the undesirable software entity.