Well if you want details you would have to understand what APIs are, details about them. I don't have the nervs to explain what APIs are Then you would have to know little about PE structure or not just PE, maybe something about DLL structure, what is the difference between executable and dynamic library. I don't have the nervs to explain what those are Then you would have to know something about pe editing, what are msstyles, how are they edited. I don't have the nervs to explain what msstyles are There are lots of thing that you need to know before you ask why. And when you read all of that you won't ask why The biggest barrier for the understanding of this problem is understanding differences between 9x and NT systems and compatibility issues. When you see what huge differences between those systems are you will understand it a bit more...