I've found that this actually happens any time Excel or Word try to open a web browser for any reason, including:
Clicking a function name in the tooltip when editing said function in Excel (to view the help article for that function)
Clicking Read article in browser when viewing any help article in the Help sidebar
Clicking on any hyperlink in a document
Clicking the ? button at the top of Backstage View (the page you start at when opening either program, or after clicking the File menu)
Clicking the ? button or any Tell me more/Learn more links in any dialog box (Help sidebar won't open while in dialog box, so tries to open a browser instead)
Pressing the F1 key while in any dialog box
Clicking Change photo or About me under User Information in the Account screen
Clicking the Manage Account button or Update Options -> View Updates under Product Information in the Account screen
Clicking View Account in the dropdown under your name at the top right
Clicking any Privacy Policy or Terms of Service link anywhere
And so on...
Now, there are certainly situations where you wouldn't want your Office applications to open hyperlinks, e.g., links within untrusted documents you downloaded from the Internet, especially those that open automatically through a scripted event in the document. But, and correct me if I'm wrong, doesn't Office already (under the default settings) warn you about those types of things? None of the situations I listed above should be blocked at all, much less terminate the entire application.
