Office 365 Accounts Hit
Not at all unexpected. Even before reading the article, there's the fact that there are so many small companies that use Office 365, for good reasons. Unfortunately, most are too small to have anything close to dedicated enterprise-level cybersecurity assets. Often, they're lucky to have one person in the office with security, or even general IT support, as part of their job description. But don't think multinationals needn't be concerned - if these small companies are cyber-business-partners, their being compromised can be a steppingstone toward a more lucrative vulnerability.
It's sad, but what is an obvious scam to those experienced in cybersecurity, can seem all too real to the intelligent, but untrained knowledge workers just trying to get through their workload. Fold the same old letter, phone, email ploys into Office 365 documents (an environment people assume secure, and where you can be called on the carpet for ignoring something that might be important), and you've increased the potency dramatically.
Yes the "tax time" feature does make these enticements more effective, but there's more to it. Get the necessary data to file a false IRS return (with false direct deposit information), and you might be able to walk off with a refund before the real entity has filed.
Another aspect mentioned in the article is the misuse of PowerShell. Power is right, but is it too much power, too easily accessible and unnecessary for most users? Again, something the big companies know to control, but users in small firms might not even know it's there.