void Main()
{
 Console.WriteLine(IsConnectedToInternet());
}

[DllImport("wininet.dll")]
private extern static bool InternetGetConnectedState(out ConnectedStateFlags flags, int reserved);

public static bool IsConnectedToInternet( )
{
    ConnectedStateFlags flags;
    return InternetGetConnectedState(out flags, 0);
}

[Flags]
enum ConnectedStateFlags
{
    INTERNET_CONNECTION_CONFIGURED = 0x40,
    INTERNET_CONNECTION_LAN = 0x02,
    INTERNET_CONNECTION_MODEM = 0x01,
    INTERNET_CONNECTION_MODEM_BUSY = 0x08,
    INTERNET_CONNECTION_OFFLINE = 0x20,
    INTERNET_CONNECTION_PROXY = 0x04,
    INTERNET_RAS_INSTALLED = 0x10
}