Adversaries may attempt to make an executable or file difficult to discover or analyze by encrypting, encoding, or otherwise obfuscating its contents on the system or in transit. This is common behavior that can be used across different platforms and the network to evade defenses.
Portions of files can also be encoded to hide the plain-text strings that would otherwise help defenders with discovery. (Citation: Linux/Cdorked.A We Live Security Analysis) Payloads may also be split into separate, seemingly benign files that only reveal malicious functionality when reassembled. (Citation: Carbon Black Obfuscation Sept 2016)
Adversaries may also obfuscate commands executed from payloads or directly via a [Command-Line Interface](https://attack.mitre.org/techniques/T1059). Environment variables, aliases, characters, and other platform/language specific semantics can be used to evade signature based detections and whitelisting mechanisms. (Citation: FireEye Obfuscation June 2017) (Citation: FireEye Revoke-Obfuscation July 2017) (Citation: PaloAlto EncodedCommand March 2017)
Another example of obfuscation is through the use of steganography, a technique of hiding messages or code in images, audio tracks, video clips, or text files. One of the first known and reported adversaries that used steganography activity surrounding [Invoke-PSImage](https://attack.mitre.org/software/S0231). The Duqu malware encrypted the gathered information from a victim's system and hid it into an image followed by exfiltrating the image to a C2 server. (Citation: Wikipedia Duqu) By the end of 2017, an adversary group used [Invoke-PSImage](https://attack.mitre.org/software/S0231) to hide PowerShell commands in an image file (png) and execute the code on a victim's system. In this particular case the PowerShell code downloaded another obfuscated script to gather intelligence from the victim's machine and communicate it back to the adversary. (Citation: McAfee Malicious Doc Targets Pyeongchang Olympics)