anti-cracking library 1.0

PECheckSum_ACLib function
Computes a checksum of exe file.

Anti-unpacking functions

function PECheckSum_ACLib(const FileName: string):DWORD;

Computes checksum of FileName by using internal algorithm (harder to detect as by using Windows API).
Returns computed checksum.

You have to store somewhere the correct CheckSum. You can store it in another file, or in FileName's header (checksum is computed only from body of EXE; header is ignored). There are several places in EXE header, where you can store it:
DOS EXE part (everywhere between MZ..PE, excluding WORD value at offset $3C-$3D), Time/Date stamp, Section Names, Checksum...