InternetGetConnectedState
BOOL InternetGetConnectedState(
    OUT LPDWORD lpdwFlags,
    IN DWORD dwReserved
);

Retrieves the connected state of the local system.
Returns TRUE if there is an Internet connection, FALSE otherwise.
lpdwFlags
Address of a double-word variable where the connection description should be
returned. Can be a combination of the following values:
INTERNET_CONNECTION_MODEM  Local system uses a modem to connect to the
Internet.
INTERNET_CONNECTION_LAN  Local system uses a local area network to connect
to the Internet.
INTERNET_CONNECTION_PROXY  Local system uses a proxy server to connect to
the Internet.
INTERNET_CONNECTION_MODEM_BUSY  Local system's modem is busy with a
non-Internet connection.

dwReserved
Reserved. Must be set to zero.