@Kinsters
Youre right on it being different systems etc that they could gain access to. Not so much on the different technology as most government places especially use the same type of computers and servers, plus the vulnerabilities to target each different kind are all readily available online, including some YouTube demonstrations.
However these hackers don't need the help. It's not just one person or even one team. This is likely multiple teams of god knows how many of them working on it. Anonymous just recently took out some Russian sites, that wasn't one person. The Russians and the Chinese had other teams targeting other companies across Europe, not just British ones. They target companies worldwide.
As for the question of are they already in, who knows. Given the threats made, and that I don't believe they are actually as good as anonymous otherwise they'd have gained access to the previous company I worked for, then I'd say they probably already are as it would take them longer to do, not a day. Hopefully that's wrong though.
If you want to look at how badly a ransomware attack for example could cripple a company, and I imagine that's what they might do (effectively hold us hostage until we remove our troops/the usual is give them money but I doubt putin wants money) then look at what happened to SEPA. They spent most of last year redoing their systems, which was of course backlogged thanks to covid so couldn't get supplies quick enough. That's where the problem will lie, getting the technology, because once a computer system has been hit with ransomware, you have to assume anything connected is also compromised. The problem there is its all connected now within one company. And sometimes even across companies if done badly.