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Microsoft update package

A Microsoft update package can be installed with wusa.exe.

Such a package consists of

Metadata
One or more .cab files of which each is one update
An XML file which describes the msu and is used by wusa.exe to perform an unattended installation.
A properties file

Extracting files and installing them

C:\> expand -f:* p:\ath\to\file.msu %temp%
C:\> pkgmgr /n:%temp%\extracted.xml