A method of preventing execution of malicious code included in program code executable by a computer system may include reading program code from a storage medium, identifying at least a section of malicious code in the program code, providing blocking code which prevents execution of the section of malicious code and attaching the blocking code to the malicious code so that the malicious code is prevented from being executed. The blocking code may instruct the computer system to skip over, rename or delete the section of malicious code, for example.