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.
On Windows, there are a variety of features in scripting languages in Windows, such as PowerShell, Jscript, and Visual Basic to make windows hidden. One example of this is
powershell.exe -WindowStyle Hidden. 
Similarly, on macOS the configurations for how applications run are listed in property list (plist) files. One of the tags in these files can be
apple.awt.UIElement, 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.
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.
Limit or restrict program execution using anti-virus software. On MacOS, allowlist programs that are allowed to have the plist tag. All other programs should be considered suspicious.
|ID||Data Source||Data Component||Detects|
Monitor executed commands and arguments that may use hidden windows to conceal malicious activity from the plain sight of users. In Windows, enable and configure event logging and PowerShell logging to check for the hidden window style.
Monitor for changes made to files that may use hidden windows to conceal malicious activity from the plain sight of users. In MacOS, plist files are ASCII text files with a specific format, so they're relatively easy to parse. File monitoring can check for the
Monitor newly executed processes that may use hidden windows to conceal malicious activity from the plain sight of users.
Monitor for any attempts to enable scripts running on a system would be considered suspicious. If scripts are not commonly used on a system, but enabled, scripts running out of cycle from patching or other administrator functions are suspicious. Scripts should be captured from the file system when possible to determine their actions and intent.