Shared...

HELP! What's going on. Am sitting in my local library, connected to wifi there, and a whole bunch of "shared" names showed up in my iTunes; I've never asked to share or be shared, went to preferences and there's nothing showing under "shared"; somehow I got rid of them from iTunes, but when I opened Finder just now, there's a nest of them showing there. 1) Why do they show up? 2) How do I prohibit them? 3) Are they able to access my computer/files?

Thanks!

Open System Preferences, click on "Sharing" and make sure you remove the checks from all the boxes that are listed there. In other words, turn off all instances of sharing. Keep in mind that whenever you're using a WiFi connection in a public place (library, Starbucks, Panera, whatever) to never access your bank, credit card info, or any other sensitive information.

1) Because they have iTunes sharing configured on their machines
2) iTunes will display shared libraries by default. If you want to make sure yours is not shared, open iTunes preferences and look under the Sharing button.
3) No. Though you should double-check and make sure you don't have anything shared (both in iTunes and in System Preferences => Sharing). If you frequently visit public networks, you may also want to enable your firewall (System Preferences => Security & Privacy).