Comment 56 for bug 1522675

 >From what I gathered, msttcorefonts and flashplugin-nonfree
> (flashplugin-installer) are affected by this, hence adding tasks for
> them.

These packages invoke update-notifier for the downloading; reassigning.

I don't see what value this sandbox user is providing, however, and why apt needs to be so noisy about it. Is this about not running the network client code as root? Clearly, anything downloaded is going to be handled as root once it's there.