[oytis]

You should either implement over-the-air updates or not connect your device to the network at all.

[yencabulator]

That doesn't help when the company behind the device disappears or stops supporting the device. Or is hacked to convert all the devices they manufactured into a botnet.

[Gud]

The problem of course is that many of these devices are eager to connect to the internet so they can often user hostile updates.