Your salary (well, last years taxable income), debts/credit rating, criminal history, address, phone number, which vehicles and properties you own and which company boards you're on.
One of organized criminals biggest income these days are scamming rich old folks because it's so trivial to get all details needed (and who to target) to be a pretty convincing bankman, IRS type agent/etc.
Some of it you have to kind of manually request at various places, but it's all available.
So data breaches aren't really that big of a deal when everything is already public.
Related:
https://www.bleepingcomputer.com/news/security/it-system-sup...
https://www.svt.se/nyheter/inrikes/cyberattack-i-datasystem-...
https://www.svt.se/nyheter/inrikes/integritetsmyndigheten-in...
Get into everything, break every security control in Europe, be a pain. As long as function is not impacted, and security problems are reported responsibly. Don't DoS a power plant because you think you can, and face a judge if you do.
That's what foreign powers are doing and slowly collecting as preparation for the future, and that's the only real way to increase cyber security across the board.
Doesn't matter what language you use if you don't actually maintain the software.
That said, I'd also prefer maintained java over unmaintained rust, so I do see your point.
Whilst we don't know exactly what they did here, a secure programming language will do bupkus when you're targeting the meatbag behind the keyboard. We need to treat people like infrastructure, that can and will eventually fail.
Unauthorized API always leaks.