Active Desktop
Active Desktop was a feature of Microsoft Internet Explorer 4.0 that added support for HTML content on the desktop, along with other features.
Significance
Malware is known to use Active Desktop settings and components for persitence.
Settings
The Active Desktop settings can be found in the Windows Registry key:
HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Desktop\General
Components
The Active Desktop components can be found in the sub keys of the Windows Registry key:
HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Desktop\Components