The security applies to the wireless function and should be enabled to keep others from hijacking your connection. It is disabled by default so that you can make sure the modem works wirelessly and then go in and enable it. There will also be a place where you can change the default admin logon name and password and there is generally a place where you can enable or disable admin functions from wireless connections. This is generally disabled by default which is why you have to make a wired connection first. If there are other users possibly within a few hundred feet or your modem, you should enable all the security and if there are several levels of security available, which is generally stated in number of bits, take the highest value, generally 24.