I have to use XP for an old CNC machine I have in my garage. I have XP (all updates and roll-up) installed in Player in win8.1 and all works well, but I need to pass files back and forth to the CNC machine which could-be on the main network. Both the Host and the Guest need Internet access, so I am left with a no-longer-secure XP and the Internet. I have the CNC XP Internet isolated on it's own ADSL modem/router and switch the ADSL line in and out as required so no cross-connections at the moment.
The CNC company has been out of business since about 2004 but this 1996 CNC machine still works fine. I am currently moving files to/from the CNC and XP via a USB thumb drive (sneaker-net), but I sometimes get the direction screwed up and overwrite a newer file. I'm old, I forget stuff. Not a big deal as both current files still exist either on XP or the CNC machine daily backups. But using a Shared Folder would overcome this problem.
I am not worried about the CNC machine as it is using proprietary software with it's own Internet access. But, if I use a Shared Folder and hook the CNC to the main network and Internet, how safe is the Host, if XP got infected with something nasty? The chances are pretty remote, but nothing in software is 100% certain these days.