Try to embed the attached test.xlsx to your Confluence page. You will notice that Confluence will have a hardtime displaying the page (CPU spikes to 100%, memory usage is over the roof, etc). In most cases, Confluence will simply crash, trying to render the viewfile macro in the background.

Workaround

Open the file in Microsoft Office, and save it as XLS instead. Then re-attach this file to a page. Notice that Confluence will be able to render the page in almost no time.