Adversaries may use hidden windows to conceal malicious activity from the plain sight of users. In some cases, windows that would typically be displayed when an application carries out an operation can be hidden. This may be utilized by system administrators to avoid disrupting user work environments when carrying out administrative tasks. 

Adversaries may abuse these functionalities to hide otherwise visible windows from users so as not to alert the user to adversary activity on the system.(Citation: Antiquated Mac Malware)

On macOS, the configurations for how applications run are listed in property list (plist) files. One of the tags in these files can be <code>apple.awt.UIElement</code>, which allows for Java applications to prevent the application's icon from appearing in the Dock. A common use for this is when applications run in the system tray, but don't also want to show up in the Dock.

Similarly, on Windows there are a variety of features in scripting languages, such as [PowerShell](https://attack.mitre.org/techniques/T1059/001), Jscript, and [Visual Basic](https://attack.mitre.org/techniques/T1059/005) to make windows hidden. One example of this is <code>powershell.exe -WindowStyle Hidden</code>.(Citation: PowerShell About 2019)

In addition, Windows supports the `CreateDesktop()` API that can create a hidden desktop window with its own corresponding <code>explorer.exe</code> process.(Citation: Hidden VNC)(Citation: Anatomy of an hVNC Attack)  All applications running on the hidden desktop window, such as a hidden VNC (hVNC) session,(Citation: Hidden VNC) will be invisible to other desktops windows.
Hidden Window
source_name: mitre-attack  url: https://attack.mitre.org/techniques/T1564/003  external_id: T1564.003     source_name: Hidden VNC  description: Hutchins, Marcus. (2015, September 13). Hidden VNC for Beginners. Retrieved November 28, 2023.  url: https://www.malwaretech.com/2015/09/hidden-vnc-for-beginners.html     source_name: Anatomy of an hVNC Attack  description: Keshet, Lior. Kessem, Limor. (2017, January 25). Anatomy of an hVNC Attack. Retrieved November 28, 2023.  url: https://securityintelligence.com/anatomy-of-an-hvnc-attack/     source_name: Antiquated Mac Malware  description: Thomas Reed. (2017, January 18). New Mac backdoor using antiquated code. Retrieved July 5, 2017.  url: https://blog.malwarebytes.com/threat-analysis/2017/01/new-mac-backdoor-using-antiquated-code/     source_name: PowerShell About 2019  description: Wheeler, S. et al.. (2019, May 1). About PowerShell.exe. Retrieved October 11, 2019.  url: https://docs.microsoft.com/en-us/powershell/module/Microsoft.PowerShell.Core/About/about_PowerShell_exe?view=powershell-5.1     