The Manifest.cab files, maintained by Microsoft, store information for determining if a newer version of a scan engine is available for download. (Each engine has an associated Manifest.cab file in its Package folder.) During a scheduled update or when Update Now has been invoked, Forefront Security for SharePoint searches the network update path for a new update. To minimize overhead, the Manifest.cab file is first downloaded and used to determine if an update is required. If an update is not required, no further processing takes place. If an update is required, the update is then downloaded and applied. When the update is finished, the new Manifest.cab file overlays the old one.
This shows the directory structure of the scan engines on a server running Forefront Security for SharePoint:
Forefront Security Install\
Data\
Engines\
x86\
Engine Name\
Package\
manifest.cab
Version Directory\
manifest.cab
enginename_fullpkg.cab
other enginename files
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Forefront Security Install is the top-level directory where all of the FSSP files are kept. This was created during the product's installation.
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Engine Name is a directory with the name of an engine's vendor (for example: Microsoft). There is an Engine Name directory for each engine.
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The Package directory contains the most recent Manifest.cab file.
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The Version Directory name has the format yymmddvvvv (year, month, day, version, for example: 0602020001). On any particular day, there may be multiple version directories. Each contains the current Manifest.cab, the enginename_fullpkg.cab (for example: norman_fullpkg.cab), and all other required files for the engine.