GetForegroundWindow

GetForegroundWindow is used to get a handle to the foreground window (the window with which the user is currently working). This function is commonly used by keyloggers and spyware to determine which window is being utilized at the moment by the user.

User32.dll

Spying Anti-Debugging

https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getforegroundwindow