Purpose
The Windows Update Agent (WUA) API is a set of COM interfaces that enable system administrators and programmers to access Windows Update and Windows Server Update Services (WSUS). Scripts and programs can be written to examine which updates are currently available for a computer, and then you can install or uninstall updates.
Where applicable
System administrators can use WUA to programmatically determine which updates should be applied to a computer, download those updates, and then install them with little or no user intervention.
Independent software vendors (ISV) and end-user developers can integrate WUA features into computer management or update management software to provide a seamless operating environment.
Developer audience
You can write WUA applications in several programming languages. WUA defines interfaces and objects that are accessible from Visual Basic, Visual Basic Scripting Edition (VBScript), JScript, and from C and C++. A familiarity with COM programming is useful to the WUA programmer.
Run-time requirements
WUA is supported starting with Windows XP and Windows 2000 Professional with Service Pack 3 (SP3). WUA is supported on the server starting with Windows Server 2003 and Windows 2000 Server with Service Pack 3 (SP3).
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Build date: 4/25/2012
Many common taks which are done with windows update api (search for updats, download and install them), with some further options, are built into in the free command line tool wuinstall (http://www.wuinstall.com), you can use it for example in a batch file without having to code the windows update API calls for yourself