Minimize any apps/webpages on it you have open (your background has to be visible), left click with the mouse, hit Personalize, and it should have Backgrounds on the page if you scroll down. You can hit Browse to look through your files on the desktop for what you want.
Answer:
This type of attack is called Malvertising
Explanation:
Malvertising (Malware Advertising) is a term in computer security that refers to the act of spreading computer malware through online advertisements. It is done by injecting malicious code into genuine online advertisement platforms or malicious webpages that appear as though they are genuine and from reputable third-party advertisers. While it is quite a new concept it is difficult to combact because content for advertisement can be placed in genuine and reputable websites that users trust.
A .xlsx file tells you that the file is an Excel workbook that utilizes XML files to create the various spreadsheets as well as macros and other hidden codes used to perform certain functions (which is why there's an X at the end; older .xls files had no indication of this external code being present, which is why they're almost never recommended for modern use).
