Query: explain T1027.016 Junk Code Insertion
Matching passage: T1027.016 Junk Code Insertion. Tactics: stealth. Description: Adversaries may use junk code / dead code to obfuscate a malware’s functionality. Junk code is code that either does not execute, or if it does execute, does not change the functionality of the code. Junk code makes analysis more difficult and time-consuming, as the analyst steps through non-functional code instead of analyzing the main code. It also may hinder detections that rely on static code analysis due to the use of benign functionality, especially when combined with [Compression](https://attack.mitre.org/techniques/T1027/015) or [Software Packing](https://attack.mitre.org/techniques/T1027/002).(Citation: ReasonLabs)(Citation: ReasonLabs Cyberpedia Junk Code) No-Operation (NOP) instructions are an example of dead code commonly used in x86 assembly language. They are commonly used as the 0x90 opcode. When NOPs are added to malware, the disassembler may show the NOP instructions, leading to the analyst needing to step through them.(Citation: ReasonLabs) The use of junk / dead code insertion is distinct from [Binary Padding](https://attack.mitre.org/techniques/T1027/001) because the purpose is to obfuscate the functionality of the code, rather than simply to change the malware’s signature.
Near-miss passage: T1027.015 Compression. Tactics: stealth. Description: Adversaries may use compression to obfuscate their payloads or files. Compressed file formats such as ZIP, gzip, 7z, and RAR can compress and archive multiple files together to make it easier and faster to transfer files. In addition to compressing files, adversaries may also compress shellcode directly - for example, in order to store it in a Windows Registry key (i.e., [Fileless Storage](https://attack.mitre.org/techniques/T1027/011)).(Citation: Trustwave Pillowmint June 2020) In order to further evade detection, adversaries may combine multiple ZIP files into one archive. This process of concatenation creates an archive that appears to be a single archive but in fact contains the central directories of the embedded archives. Some ZIP readers, such as 7zip, may not be able to identify concatenated ZIP files and miss the presence of the malicious payload.(Citation: Perception Point) File archives may be sent as one [Spearphishing Attachment](https://attack.mitre.org/techniques/T1566/001) through email. Adversaries have sent malicious payloads as archived files to encourage the user to interact with and extract the malicious payload onto their system (i.e., [Malicious File](https://attack.mitre.org/techniques/T1204/002)).(Citation: NTT Security Flagpro new December 2021) However, some file compression tools, such as 7zip, can be used to produce self-extracting archives. Adversaries may send self-extracting archives to hide the functionality of their payload and launch it without requiring multiple actions from the user.(Citation: The Hacker News) [Compression](https://attack.mitre.org/techniques/T1027/015) may be used in combination with [Encrypted/Encoded File](https://attack.mitre.org/techniques/T1027/013) where compressed files are encrypted and password-protected.