Which technique is NOT part of malicious code protection?

Data Encryption Standard (DES) does not qualify as a technique specifically aimed at protecting against malicious code. Instead, DES is primarily an encryption mechanism used for securing data by making it unreadable to unauthorized users. Its main purpose is to ensure confidentiality of data during transmission or storage. While it is essential for protecting data integrity and confidentiality, it does not address the detection or prevention of malicious code execution, which is the focus of the other techniques listed in the question.

In contrast, sandbox techniques create isolated environments to run untrusted code so that if it behaves maliciously, it won't affect the overall system. The No Execute (NX) bit is a hardware feature that prevents the execution of code in certain memory regions, thus protecting against buffer overflow attacks that inject malicious code. Stack corruption detection involves mechanisms to identify and respond to unauthorized changes in the stack memory, which is crucial for identifying attempts to execute harmful code.

This understanding solidifies why Data Encryption Standard is the correct answer as it does not directly relate to the protection mechanisms against malicious code compared to the other options provided.