This disclosure is directed to software modification that may be used to prevent software piracy and prevent unauthorized modification of applications. In some embodiments, a software vendor may modify software prior to distribution to a user. The software vendor may extract cutouts from an application to create a modified application. The modified application and the cutouts may be downloaded by a user device. The user device may run the application using the modified application and by executing the cutouts in a secure execution environment that conceals the underlying code in the cutouts.