var
  MessageBoxANext  : function (hWnd: HWND; lpText,    lpCaption: PAnsiChar; uType: UINT): Integer; stdcall;

function MessageBoxACallback(hWnd: HWND; lpText, lpCaption: PAnsiChar; uType: UINT): Integer; stdcall;
begin
  Result := MessageBoxANext(hWnd, lpText, 'Message From Dll', uType);
end;

procedure DllMain(dwReason: DWORD);
begin
 case dwReason of
   DLL_PROCESS_ATTACH: begin
                           HookAPI('user32.dll', 'MessageBoxA',
                             @MessageBoxACallback,       @MessageBoxANext);

                       end;
   DLL_PROCESS_DETACH: begin
                           UnHookAPI('user32.dll', 'MessageBoxA',
                             @MessageBoxANext);
                         end;
 end;
end;

begin
 DllProc := @DllMain;
 DllMain(DLL_PROCESS_ATTACH);
end.

function ProcessInjectLibrary(PID: DWORD; lpszLibName: PAnsiChar): Boolean;stdcall;