I don't use Office 365, but I assume they have cloud storage for all your documents? I'm sure there are a few users who have backed up their seeds by putting them in a document and saving them to the cloud. I'm sure there are also plenty of users using the exact same username/email and password for Office 365 as they use for some crypto web wallet. It all depends on what data have actually been breached, but if it is Microsoft, I wouldn't be surprised if this leads to some crypto scams as well.
That's one reason why I've *always* been opposed to medical records being stored online, and the computer systems used in hospitals and many other medical institutions do this
So the software involved in this breach is called PACS, which stands for Picture Archiving and Communication System. This software is massive. It is used almost globally, including throughout the US, Canada, Mexico, Europe, China, India, Japan, South Korea, Middle East, Australia, and South America. I couldn't even take a guess at just how many medical images from how many patients are stored on this system, but 1.2 billion is likely a small fraction.
The US is the biggest part of this leak, with almost 800 million images coming from there. Other large contributors are India, Brazil and South Africa. It's also worth pointing out that some countries, most notably European countries like Germany and the UK, have their PACS servers disconnected from the internet and run on their own secure network, and so are protected from this kind of breach.