Help and Support Centre is the default application provided to access online
documentation for Microsoft Windows. Microsoft supports accessing help documents
directly via URLs by installing a protocol handler for the scheme "hcp",
a typical example is provided in the Windows XP Command Line Reference,
available at http://technet.microsoft.com/en-us/library/bb490918.aspx.
Using hcp:// URLs is intended to be safe, as when invoked via the registered
protocol handler the command line parameter /fromhcp is passed to the help
centre application. This flag switches the help centre into a restricted mode,
which will only permit a whitelisted set of help documents and parameters.
This design, introduced in SP2, is reasonably sound. A whitelist of trusted
documents is a safe way of allowing interaction with the documentation from
less-trusted sources. Unfortunately, an implementation error in the whitelist
allows it to be evaded.
Read all about it here...
Or here..
