1. A method of managing a whitelist that at least partially governs operation of a computational system, the method comprising: providing a computer readable encoding of the whitelist, wherein the whitelist identifies (i) instances of code that are allowed to execute on the computational system and (ii) trust attributes therefor, wherein at least one of the trust attributes indicates, for a trusted one of the code instances, that a further code instance introduced into the computational system based on execution of the trusted code instance is to be added to the whitelist and thereby allowed to execute; responsive to execution of a first code instance that at least initiates introduction of an executable second code instance into the computational system, checking a whitelist entry that corresponds to the first code instance and, based thereon, extending the whitelist to allow execution of the second code instance only if the whitelist entry includes a trust attribute; and executing on the computational system only those code instances allowed by the whitelist; wherein relative to the first code instance and the second code instance, the extending the whitelist comprises adding an entry comprising: a size of a file from which the second code instance may be loaded into memory and executed; a name of the file or a path thereto; and a hash, a digital signature, authentication code, checksum, fingerprint or other cryptographic digest usable to verify integrity of the file.