I am a little concerned. I have a new Windows 10 Laptop, where I put some copnfig files from my desktop PC via good ol' windows shared folder (I'm not quite sure about the english translation). I forgot to unshare it afterwards. I noticed today when I was in a public network (at university) and when I unshared it, it said there was a user connected to it. Since it was in a informatics course with 150 might-be hackers around me, I panicked a little. When i checked netstat there was still some connection going on. So I shut the system off asap.
Probably the user in the shared folder was just me and the connection was supposably some browser window in the background.
But it made me wonder, which security risks are you taking if you have a shared folder with write permission in a public network?