I ment making the checksum from the codebase..
Originally Posted by matsp
I think it's quite feasible to overwrite NOPs in code to insert other code, but there are certainly plenty of other methods for subverting code in an application. Overwriting parts of it with NOP's would be another possibility.
Originally Posted by Bubba
0x66 is a prefix in x86, which toggles 16/32-bit registers.
The two bytes of 0x66 0x90 is a NOP (exactly, it is "xchg ax, ax" in 32-bit, and "xchg eax,eax" if you execute in 16-bit mode - but since xchg doesn't actually do "anything" when both sides are the same register, it's a "NOP", and someone at Intel in the late 70's/early 80's decided that "NOP" should be the opcode of "xchg ax,ax". Multiple 0x66 prefix are also supported by the processor, as long as the total number of bytes is less than 15.
I agree, there's many other ways you could manipulate what the code in a game does, without inserting or removing NOP instructions.