Can the WiFi on ESP8266 be disabled? I've been reading a lot on the ESP8266, but still my understanding is shaky. I have the Arduino IDE running on a PC, which uses wires to connect to the ESP8266 via a USB device (Device Manager > Ports (COM &amp; LPT) > Silicon Labs CP210x USB to UART Bridge). This is how I uploaded a simple sketch to the ESP8266.

It works and has been installed in the wall. I'm happy and relieved to complete the project... except for one small thing: I noticed that it shows up on WiFi. I can connect to it without a password, with a "Limited" connection. After that I'm lost, but I wonder if someone who knows what they are doing can use this unsecured connection to hack my install. I'd like to disable the WiFi, if possible, since I'm not using it.

The worst part is my learning curve now starts over. I thought that when my sketch gets uploaded, it replaces the original firmware. Now "firmware" is an elusive concept. I keep thinking that it shows up on WiFi because of something running in firmware. My sketch hasn't any code for WiFi. What am I missing/do I have wrong?
To turn of the WiFi add the WiFi library and use WiFi.forceSleepBegin();

Firmware is the program/sketch that controls a MicroController Unit aka MCU (and in this case a Arduino).
Best explanation I know is here: https://en.wikipedia.org/wiki/Firmware