Thank you for posting your query in the Community. I believe by "open network" you mean the Guest Network. It appears to be unsecured however, it would prompt for the Guest password once you open a web browser.
You can log into the modem and disable your Guest Network from the Wireless/Guest Network menu. You can follow the walkthroughto log into the modem and navigate to Guest Network to disable it.
If you need assistance to disable the Guest Network, please send us a private message at @CommunityHelps. Our private messaging system is explained in this blog.