1. A method of managing a whitelist that at least partially governs operation of a computer system, the method comprising: (a) storing a computer readable encoding of the whitelist on the computer system, wherein the whitelist comprises: (I) a first whitelist entry associated with a first code instance; wherein the first whitelist entry comprises: (i) a trust-execute attribute that allows the first code instance to execute on the computer system; and (ii) a trust-changes attribute that allows at least a third code instance, introduced into the computer system via the first code instance, to be added to the whitelist; (II) a second whitelist entry associated with a second code instance, wherein the second whitelist is absent of a trust-changes attribute; (b) responsive to an attempt by the first code instance to introduce the third code instance into the computer system: (i) checking the first whitelist entry for the presence of the trust-changes attribute and, based thereon; (ii) extending the whitelist to include a third whitelist entry associated with the third code instance; wherein the third whitelist entry comprises: (i) a trust-execute attribute that allows the third code instance to execute on the computer system; and c) responsive to an attempt by the second code instance to introduce a fourth code instance into the computer system: (i) checking the second whitelist entry for the presence of a trust-changes attribute; (ii) determining that the second whitelist entry is absent of a trust-changes attribute; and (iii) denying the extension of the whitelist to include a fourth whitelist entry associated with the fourth code instance; (d) executing on the computer system only those code instances allowed by the whitelist; wherein, the checking (b)(i) and (c)(i), extending (b)(ii) and executing (d) steps are performed by the computer system.