A Phishing scam designed to trick you into providing your Microsoft account login and password
This is a particularly well designed scam that has caught out many people
This is because it uses a verified Microsoft Account of one of your contacts.
So you are more likely to trust the message
And it is much less likely to be marked as Junk.
The email arrives worded something like this:
Subject: Fred Bloggs shared the folder "Bloggers Limited" with you
Note: replace "Fred Bloggs" and "Bloggers Limited" with a contact you know (and probably trust)
The content reads something like this: