Hi kristy bailey-prouty,
Welcome to post in Microsoft Community. I'm Mosken, let me help you figure it out.
According to your description, I knew that you cannot install the latest Security update.
First of all, we're sorry, we've recently received reports similar to yours. This is because the update itself needs to be further refined, and we recommend that you ignore the update for now.
We have reported this issue to the relevant departments and will resolve this issue as soon as possible, please don't worry too much.
Or you can report this event to Microsoft in the "Feedback Hub" application(launched by "Win" + "F") which Windows built in, and the developers will try their best to solve the problem.
Additionally the XML file format is a metalanguage which allows users to define their own customized markup languages, especially in order to display documents on the internet. You can't open it with Excel (although its suffix is similar to xsl), but you can open it with Notepad.
The above steps are provided based on the information I have learned so far, I wish that will be helpful to you. If your problem still cannot be solved by these steps, you could tell me the specific situation in the next reply. I will continue to assist you in solving the problem.
Best Regards,
Mosken- MSFT | Microsoft Community Support Specialist