Software program self-modification

TL;DR: The Rewriter Module as discussed by the authors provides a mechanism for modifying an executable upon first execution, such as attaching a unique serial number, encrypting or decrypting the executable, or adding protection code (license enforcement code) to the executable.

Abstract: The present invention, generally speaking, provides a mechanism for modifying an executable upon first execution. Various modifications may be made to the executable, including modifications useful for purposes of electronic software distribution, such as attaching a unique serial number, encrypting or decrypting the executable, or adding protection code (license enforcement code) to the executable. A Rewriter Module performs the actual modification. First, a copy of the executable is made. The copy is then run and the original executable is deleted. Then a second copy of the executable is made using the name of the original executable, and the first copy is deleted. During one or both of the copying steps, modifications are made to the executable. The modifications may be modifications useful for purposes of electronic software distribution, especially Try/Buy. When a software product is purchased, the foregoing process may be reversed, leaving the executable in its original "pristine" condition. All of the foregoing activity is transparent to the user.