License & Copyright protection tools for Visual LISP applications ?

I red that theme last week, it was really interesting

I Have a cuestion.

I have programed lisp since 7 years ago, so that I have so many program for
Urban Design.

But I'm architect, not programer.

So that I know I´m a beginner. But sometimes I have shared some of my
programs with my friends, I have never received money for.

But I have written a protection function which is located at the beginning
of the file: "LandUtilities.VLX" It needs DosLib

What do you think about this primitive protection lisp function?
What as easy can it be cheated?

Sorry because of my poor english

JPadilla
----------------------------------------------------------------------------
----------------------------------------------------------------------------
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(DeFun LU:TestRegisteredComputer (#LiReC / #InDaL #StMeL)
(SetQ
#StMeL (StrCat "LU-" (SubStr (GetVar "AcadVer") 1 2))
#InDaL (CDR (CAR(DOS_FileDate (FindFile "LandUtilities.VLX"))))
);SetQ
(If
(Member
(List
(DOS_Computer)
(DOS_SerialNo "C:\\")
(vl-registry-read
"HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\""Product
ID")
(vl-registry-read
"HKEY_LOCAL_MACHINE\\HARDWARE\\DESCRIPTION\\System\\CentralProcessor\\0"
"ProcessorNameString")
);List
#LiReC
);Member

(If
(And
; Periodo de Licencia
(And
(> #InDaL 20031231); después de
(< #InDaL 20040331); antes de
);And
; última compilación mas 1 meses y menos 1 mes
; Debe ser actualizada a principio de año
(And
(> (GetVar "CDate")(- #InDaL 100))
(< (GetVar "CDate")(+ #InDaL 100))
);And
);And
();(PrompT "\nOK Period");La Licencia está vigente
(ProgN
(DOS_MsgBox "Contacta a Jesús Padilla\"
"Land Utilities ha expirado" 1 2)
(VL-CmdF "MenuUnLoad" #StMeL);VL-CmdF
(DOS_CloseAll)
(Exit)
);Progn
);IF
(ProgN
(DOS_MsgBox "Contacta a Jesús Padilla\"
"Land Utilities no ha sido registrado" 1 2)
(VL-CmdF "MenuUnLoad" #StMeL);VL-CmdF
(DOS_CloseAll)
(Exit)
);ProgN
);If
);DeFun

(LU:TestRegisteredComputer
(List
'("PMA-A1""8CE55C50""55690-OEM-0011903-00102"" Intel(R)
Pentium(R) M processor 1600MHz")
'("CAD-A1""F009175D""55690-OEM-0014295-28326"" Intel(R)
Pentium(R) 4 CPU 2.40GHz")
'("CAD-B1""A853AE14""55274-640-0000356-23309""AMD Duron(tm) ")
'("CAD-B2""DC6D0DE8""55686-OEM-0045397-53164""Intel(R) Celeron(TM) CPU
1200MHz")
);List
);LU:TestRegisteredComputer