plz suggest security for DLL functions

[Gaurav Kumar <gkverma () gmail com>]

friends, 

We are developing a software that makes use of a COM DLL. The whole
logic lies in the dll. The User Interface is in VC++. DLL exposes
functions, application calls it and displays result. Now, we found
that anybody can copy the DLL, register it and make use of those
functions.

Please guide us in making those functions secret or encrypted so that
others cannt use our functions.

thanks and regards,
gaurav
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