Shared IP address in Public places?

When I work in a public place with open Wifi, such as Coffee shops, sometimes a small alert pops up with the message telling me "Another device is using your IP address".
What does this mean? Some one is hacking in my computer?
All I am doing is to go under System Preferences /Sharing and make sure the only folder visible to others is Public.
I am not very familiar with the function of IP address. Do I need to be worried about this?
Thanks

This is common issue with public networks where the duration a device is connection varies widely and as such IP address conflicts are frequent, but absolutely nothing to worry about. Usually after you get the warning, you end up getting a different IP address and you can go about your way.

No one is hacking you or anything.

Now when it comes to using public WiFi though, you need to be wary of what sort of things you do, so make sure that no sharing (file/screen/web other otherwise) is enabled so that no one can see anything from your machine. Ensure that if you HAVE to do any banking or anything that you are doing it through a HTTPS connection. Ideally, you want to avoid banking or other financial related stuff on public WiFi..

If you rely heavily on public WiFi for your general Internet access, you might want to research some affordable VPN solutions that will keep you and your data secure..

"Now when it comes to using public WiFi though, you need to be wary of what sort of things you do, so make sure that no sharing (file/screen/web other otherwise) is enabled so that no one can see anything from your machine. "

Thank you so much-
I am not doing any banking in public- But please let me ask you , if I want to check the sharing status, the only place I need to be checking is under SystemR/sharing ???
That said, do I need to disable bluetooth sharing on my computer as well? It is supposed to ask me for permission before accessing.

Thanks again

Yes, System/Sharing is the place you want to go and check. I'm not sure how Bluetooth sharing is supposed to work, but presumably it will have some sort of authentication. But to be on the safe side, you're just better of disabling it all and re-enabling them on your home network if you use any of the sharing services..