[anon_cow1111]

Random mint 18.04 user here.

I just noticed about a week ago that flatpak was downloading huge amounts of data (like hundreds of MBs). I had all system updates set to download and install manually, and hadn't installed anything new for at least a month. All this data was getting sent to /var/tmp as flatpak-cache folders.

I don't know what it was doing but I've since turned it off in the startup list. Any ideas? What are the chances this was malicious?

[c487bd62]

I'm not a flatpaker but maybe it was updating the runtimes? http://docs.flatpak.org/en/latest/available-runtimes.html

Honestly I would be more worried about running mint (a topic not suited for this thread, a quick search would probably show you what I've read about it in the past).