How can I exclude by file extension?

I want to exclude, for example, *.abcd files in any folder from scans.  Is it not possible to do this?

If I add *.abcd as a file exclusion, it does not work and still scans the files.  I can't use folder exclusion because the folders contains other files that I do want to be scanned.

These *.abcd files are scattered across several directory structures.  There should be a simple and intuitive way to configure this exclusion.

Thanks!