After Microsoft Suffers Mega-Breach, What Can Customers Do?

Warnings: Products' Source Code at Risk, Customers' Secrets Spilled via Email
What did Microsoft mean when it said that nation-state hackers are "attempting to use secrets of different types" they found in its emails with customers, what's the risk posed by those attackers also accessing Microsoft's source code and what can - and should - customers do about it all?

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