This question has been covered several times.
There are some things you can do to limit what is visible and accessible thru PMS.
First, pick out, and share only specified folders/files rather than ALL folders/files. Go to the Navigation/Share settings tab, and go to the box at the bottom. Select only the files/folders you want to share. Default is for PMS to share all folders/files <All files> on your serving PC, and it will even display 'hidden' folders/files that are not visible in Windows Explorer. You can also add folders/files from other PC's or NAS within the network that are Windows shared, so your PS3 can pick those up as well.
Second. If you only have one DLNA compatible device, your PS3, you can add it's IP to the IP filter box on the the General Configuration tab. PMS will then reject all other IP's and only serve/display the folders/files of your choosing (Step 1 above) to your PS3 only.
Third, if you check the Additions and Plugins forum, I believe there is someone working on something with passwords, if I recall correctly. If I find it, I'll repost.
Fourth, and most importantly, PMS only serves within the LAN, to other DLNA compatible devices on the same subnet. The only time it reaches out, into the WAN, is if you use the web streaming option, and it is to browse/view online files..............not to serve them to others. That's the way I understand it, unless some other crazy stuff has been developed in the last while.
Val Killmore: Potato Chip Assassin
SubJunk53--Java 7u4--Acer Aspire 6930 2CoreDuo @ 2.00 GHz 3.00 GB RAM serving to : PS3 Slim -- 2 Xbox360