Basically, there was a security flaw with Microsoft’s Internet Information Services (web server software) that could be exploited by an attacker to gain access to files and folders they shouldn’t be able to (permission escalation?). Well, instead of providing an actual fix to the problem as a whole, they applied a bandaid fix by creating a new folder named “inetpub” on peoples system drive, and apparently the presence of the folder is able to prevent the exploit from working. People noticed the folder and deleted it because they thought it was being created by an attacker, so Microsoft had to tell people not to delete it.