Abstract: Dynamic run-time verification of a module which is loaded in memory (in whole or in part) for execution is enabled by using pre-computed portion-level verification data for portions of the module smaller than the whole (e.g. at the page-level). A portion of the module as loaded into memory for execution can be verified. Pre-computed portion-level verification data is retrieved from storage and used to verify the loaded portions of the executable. Verification data may be, for example, a digitally signed hash of the portion. Where the operating system loader has modified the portion for execution, the modifications are reversed, removing any changes performed by the operating system. If the portion has not been tampered, this will return the portion to its original pre-loaded state. This version is then used to determine validity using the pre-computed portion-level verification.