@GrahamGo: While suspicious because of the update, that sounds more like a bad cable/flaky USB controller. Check with another data cable, and on another computer if possible?
Also, because it's actually relevant here, and I have to say it:
Have you tried turning it off and on again? (Seriously, restart the device and your computer
).
As for the rest: yup. BackDoorLock does just that. (As well as the BBB firewall filters, although as a 'side effect' of their main purpose
).