Beaglebone green WiFi Hotspot/Tether disable

Beaglebone green has a WiFi Hotspot/Tether enabled by default

It has no password and so is unsecure
Is ther a way to set password or else disable this functionality

Yeah, there is a whole bunch of confusing suggestions on internet for Debian, Ubuntu, Raspberry Pi etc… I assume you connect to the board via the USB with ssh debian@beaglebone.local and want to just disable the WiFi access point, then do this:

# for current status
$ ip link
# or
$ ip addr
...
6: SoftAp0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
# <--- that's your WiFi access point
    inet 192.168.8.1/24 brd 192.168.8.255 scope global SoftAp0
# <--- and that's the address of the BB on its own Wifi network

# to shut it down:
$ sudo ip link set dev SoftAp0 down

Then it should disappear from the wifi list on your phone, and the status should be down:

$ ip link
...
6: SoftAp0: <BROADCAST,MULTICAST> mtu 1500 qdisc mq state DOWN mode DEFAULT group default qlen 1000

Also, the same with the nice and legacy ifconfig:

$ ifconfig # for the status
$ sudo ifconfig SoftAp0 up
$ sudo ifconfig SoftAp0 down