user55517: I bought several ESP8266 boards from an Amazon seller, and I have flashed them with custom firmware.  This firmware basically sends telemetry to an MQTT server, and has some OTA functionality to self-update from a web server I run.
I flashed them from the Arduino IDE initially, although have also since updated them OTA.
These devices properly connect to the AP I have defined, get an address, and send their mqtt messages.  However, they ALSO advertise an SSID that is FaryLink_XXXXXX where the XXXXXX relates to the MAC.
How is this possible, and how should I wipe their little brains fully?

user37622: The Espressif ESP8266 SDK is part of every Arduino sketch for the ESP8266. The SDK handles the WiFi and other basic functions of the chip.
If enabled, the SDK remembers WiFi STA and SoftAP settings and start to connect right after boot. At default it is enabled. In Arduino sketch this is controlled by WiFi.persistent(bool) and of course this setting is stored too.
To clear SoftAP settings, call WiFi.softAPdisconnect(). To only turn off SoftAP, use WiFi.setMode(WIFI_STA).

55517: <p>I bought several ESP8266 boards from an Amazon seller, and I have flashed them with custom firmware.  This firmware basically sends telemetry to an MQTT server, and has some OTA functionality to self-update from a web server I run.</p>

<p>I flashed them from the Arduino IDE initially, although have also since updated them OTA.</p>

<p>These devices properly connect to the AP I have defined, get an address, and send their mqtt messages.  However, they ALSO advertise an SSID that is <code>FaryLink_XXXXXX</code> where the XXXXXX relates to the MAC.</p>

<p>How is this possible, and how should I wipe their little brains fully?</p>
 37622: <p>The Espressif ESP8266 SDK is part of every Arduino sketch for the ESP8266. The SDK handles the WiFi and other basic functions of the chip.</p>

<p>If enabled, the SDK remembers WiFi STA and SoftAP settings and start to connect right after boot. At default it is enabled. In Arduino sketch this is controlled by <a href="https://arduino-esp8266.readthedocs.io/en/latest/esp8266wifi/generic-class.html#persistent" rel="nofollow noreferrer"><code>WiFi.persistent(bool)</code></a> and of course this setting is stored too.</p>

<p>To clear SoftAP settings, call <code>WiFi.softAPdisconnect()</code>. To only turn off SoftAP, use <code>WiFi.setMode(WIFI_STA)</code>.</p>
