After I create my Internet.Application object using _IECreate, I use the following DLL call to change the user agent: Description in API: HRESULT UrlMkSetSessionOption( DWORD dwOption, __in_bcount_opt(dwBufferLength) LPVOID pBuffer, DWORD dwBufferLength, __reserved DWORD dwReserved ); dwOption [in] An unsigned long integer value that contains the option to set. This can be one of the following values.