Originally Posted by HarryT
No, because a book can only be downloaded to a Kindle (or whatever) that is registered to your account, and you're going to notice if a device that you know nothing about suddenly appears in your device list.
There's download to PC option which lets you pick an existing device as the target (so the DRM can be applied) but doesn't need a desktop reading app registered so could occur from anywhere. I'm pretty sure you can remove a device from your account with a few clicks too, which you'd assume they'd do after pilfering your entire library even if they did register a device.
Also consider, you can use a kindle and buy books for years without ever logging in and looking at what devices you have registered if you're buying from the device itself.
Not saying it's likely, in fact I find it rather unlikely, but it's a possibility and that does mean someone could be receiving hefty fines when they've done no wrong.