Activity Monitor data being received by unseen process?

I don't do any torrents.

Not accustomed to malware on my Mac, but I'm going to grab a copy of Malware Bytes and give that a go. An app that is hiding itself from Activity Monitor and is chewing through that much data might be malware.

EDIT: No malware found. I mean, I guess that's good news, but it doesn't explain the data.

My family and I barely use half of the terabyte of data on our plan in a typical month. It's not worth it to me to pay for unlimited. I don't use that much normally. Also, all updates are installed. Nothing is downloading.

That said, I think you misunderstood my question. I'm not asking to turn things off or how system processes work or whether any of them are necessary. I have 28 years of experience working in IT. I know how all this works. I'm saying that I see data being received at the bottom of the Activity Monitor steadily, but no app in the process list is increasing. It's as if something is using data in the background but isn't showing up on the process list.

The 610.5 MB in the screenshot below is steadily ticking upward right now, as I type. You can see that happening in the graph. The data received numbers in the list of processes are completely static. This doesn't make sense to me. The Activity Monitor is simultaneously telling me that no processes are receiving data, but also telling me that data is continuously being received in fairly large quantities.

How do I troubleshoot data being received when I can't see what process or app is doing it?

So, I walked away for about a half-hour after I posted that and came back, and now the data received in the summary is at 803.7 MB.

A couple of the processes on the list have increased a few MB, but nothing even comes close to accounting for almost 200 MB of data received. And this was while the machine was idle with no apps running.

This makes no sense.

EDIT:

In the last 10 minutes, it jumped to 1.10 GB! No activity is shown in the process list. This is frustrating!

I guess I'll have to go through all that. Was hoping the Activity Monitor would do what it's supposed to do and I could address the process directly. I'm not sure why Apple would allow a process to use network data without showing it in the AM, but whatever. Googling this issue, it looks like I'm not alone with this mystery. Others have complained about mystery data usage.

Anyway, thanks for the link.