Universally known to whoever wanted to intercept that traffic.
Maybe and hopefully not known to the staff of those networks (the current staff could be maintaining what somebody else set up) as some of those companies fixed the problem when contacted by the researchers.
For sure not known to me and a lot of other people. I believed that everything in digital streams was encrypted. Ok, those ATM connections are probably tech from the 90s, but they probably had upgrades in part because of regulations. Privacy, security, nothing?
It's an interesting problem. The reality is that for any decently-sized business people don't really know their networks. Their assumptions are sane, but often simply incorrect. I've heard a lot of people say things like "well the traffic is not going externally, so it's fine to leave it unencrypted." It's a bold, and almost always unchecked assumption.
It doesn't help that practising even reasonable security comes at such a cost many orgs find reasons to not justify doing it - we've spent decades creating systems that are difficult to secure at every level and hand waving it away and now it's a wobbly jenga tower of systems.
This is a major issue I have with cybersecurity articles. They're often quite clever and interesting, but the real companies I've worked for can barely implement SSO, MFA, software updates, pay for logging, write worthwhile detections, etc. The basics are quite well understood, but no one seems to acknowledge that hardly anyone can actually manage the basics.
My experience as well, my background is enterprise development - mostly what would be classed as the M in SME (Small-Medium Enterprise) with forays into the big E and all of them fell down on even basic security in so many many ways.
Example: at the largest place I worked (5000 staff, 200 in Dev/QA) I found out by accident that the outsourced devs where using personal laptops when in a sprint meeting I asked where someone was and got back "His work machine died, he's nipped home to get his personal laptop".
That company constantly raved about how good it's security posture was...
I spoke to my oppo number on the IT/platform team and his response was "yeah we know that happens, I've been trying to get them to ban it/make it impossible for a while".
Even when the assumptions are correct, you’re depending on people doing their jobs correctly.
Over the years, I’ve found shockingly bad failures, usually on areas of internal networks where there is ambiguity as to what internal org is responsible. In old companies with data centers and cloud, there’s often pretty bad gaps.