1. A hook interface module cooperable with a program whose functionality is to be modified and with at least one module providing said modified functionality, said program including at least one symbol indicating a respective point in said program execution where modification is permitted, said hook interface module comprising: means for resolving an address for the at least one symbol; means for maintaining a respective list indicative of any modification functions associated with each of the at least one symbol; registration means for enabling said at least one module to register a modification function for a symbol with said interface module including means for adding an indicator for said modification function to the list for said symbol; arming means for enabling said at least one module to arm at least one modification function associated with a respective symbol including means for modifying the contents of the address for the at least one respective symbol to cause program execution at said at least one respective symbol address to jump to a location in said hook interface module; and dispatching means, responsive to program execution jumping to said hook interface module, for causing program execution to, in turn, jump to any modification function associated with a symbol from which program execution has jumped.