How to find source and targhet of data transmissions

[Bret Busby]

Hello.

I am running UbuntuMATE 16.04.x.

For the past few minutes, the System Monitor shows data being
downloaded, that I have not authorised, and about 300-500 kB/s.

How do I find where the data is originating, and, what is downloading it?

Thank you in anticipation.

-- 
Bret Busby
Armadale
West Australia
..............

"So once you do know what the question actually is,
 you'll know what the answer means."
- Deep Thought,
 Chapter 28 of Book 1 of
 "The Hitchhiker's Guide to the Galaxy:
 A Trilogy In Four Parts",
 written by Douglas Adams,
 published by Pan Books, 1992

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