1. A method, comprising: executing, by a multitasking processor in a foreground, a first program module, the executing including accessing a table of address correspondence between the multitasking processor and a memory storing instruction lines of multiple program modules; transitioning from foreground execution of the first program module by the multitasking processor to foreground execution by the multitasking processor of another program module of the multiple program modules; calculating a first signature based on at least some instruction lines of the first program module stored in the memory; and transitioning to foreground execution of the first program module, the transitioning including: calculating a second signature based on the at least some instruction lines of the first program module stored in the memory; comparing the first signature to the second signature; and preventing execution of instruction lines of the first program module stored in the memory by the multitasking processor based on the comparing.