OK, thank you for explaining the situation so I can understand..
First, it is no possible for anyone to "login" and steal your information on the iPhone only based on it being connected to an unsecure WiFi network. A "hacker" would have to get you to install an application (from the App Store) that would somehow access your notes (and you'd be warned of this attempt) and then forward that along.
If you weren't entering any of your credit card information while connected to the unsecure network then no problem there..
If you always ensure to use HTTPS sites before entering your credit card information, it's very hard for people to get your numbers from that transaction. I use my credit cards online all the time and have never had anyone steal it. The one time it HAS happened was at a physical location where I swiped my card and the clerk wrote down the number..
The other way someone could've gotten your credit card information is hacking any of the sites you have visited who store your information..it doesn't necessarily have to be coming FROM your computer..
Last, there is no good way of KNOWING you have spyware installed on the computer because that would just be counter to how spyware should operate. It'd be pretty silly for a spyware/malware write to have their applications show up in Activity Monitor with obvious names that would tip anyone off..
Additionally, if your home network is secure, then only people you trust (who have the password) could've gotten access to your machine..or you installed some programs from potentially shady sides that claimed to be legitimate or what have you..if neither of these is true, then no worries.
Finally, as long as your running as a regular user with admin privs on your computer, any software installation that makes system changes will require your admin privs to complete, so if you haven't seen that recently (or at least right around the time the credit card numbers were stolen) then your Mac isn't the place for you to be looking..