>Since I have never heard about Log4j before they sent me this email, clearly my app does not use it.
>I just can't understand how an application that I wrote, 100%, could use a technology that I have never even heard about before. If .NET uses this technology, I am sure MS will defend me <g>

This has never been a wheelhouse of expertise for me, though I would think you'd want to know the picture of the infrastructure your app is running on.

Beyond that, I think Al has given some good general advice.