Different Smart WiFi subscribers in an area are in a single shared LAN, like PCs connecting to a repeater hub. Thus as John Paul points out, you can access shared folders on the other PCs, or do worse.
Personally, I’ve tried “wardriving” programs on a laptop. They detect Smart WiFi access points. “Wardriving” is driving around, looking for open WiFi hotspots. This was a few months ago, and at that time, Smart WiFi was not encrypted at all. I could see the data being sent to the subscriber nodes. I recall seeing web, Chikka messenger, and Yahoo messenger traffic.
I did that while on a laptop, connected for a short time. What more if you’re connected fulltime to Smart WiFi?
One solution is to not connect the PC directly to the Smart WiFi equipment. Instead, connect a router so that your PCs inside will have their own private network separated through Network Address Translation (NAT).
Smart should educate their subscribers, or better yet, fix the system to avoid these problems (on top of the other well-publicized problems).