A method of validating software including maintaining, in a trusted computing system, a copy of at least portions of data of the software, the software comprising data in an untrusted computing system. The method includes, with the trusted computing system, specifying selected data from data included in the copy as hash data, generating an executable file for generating a hash based on the specified hash data, executing the executable file to generate a check hash using the specified selected data from the copy as the hash data, and determining whether the software is valid based, at least in part, on a comparison of the check hash to an access hash generated by execution of the executable file by the untrusted computing system using the specified selected data from the untrusted computing system as the hash data.