There is good advice on this thread, and some misinformation as well.
I work in the field and have to advise on this stuff often.
The most common, and simplest, form of gathering information is key loggers on public computers; Web cafe's, libraries, hotel lobbies etc. are easy targets. Enter only information into them that you would willingly share with a stranger on a bus.
A second, common, form of stealing credit card numbers is logging into pay wifi sites. You can find these false logins in public places; hotels, airports and so-on. You login thinking you are connecting to a hotspot by entering your credit card number and security code. There goes your credit card information.
Key loggers, viruses, wifi and ethernet sniffing are highly unlikely if you use your own equipment and an SSL connection. The latter methods are not needed on public terminals. Point being, avoid public terminals as they are often logged.
One further word of warning about public terminals. Only open attachments that contain information you would share with a stranger on a bus. When you open an attachment, it is downloaded (unprotected) to the terminal and may be accessible to others. For example, you download and view your e-mail over a secure connection and view a Word Document of a confidential work project. This file is saved in a 'temporary' location and may not be cleaned up when you log out. You *think* you were secure, but you have just shared that information with a nefarious ne're do well.
As for viruses... well... If you can't trust your operating system, nor your firewall, nor your antivirus software, perhaps you shouldn't be paying them for software that is poorly designed and insecure?
Last edited by JordanH; 02-17-2012 at 10:30 PM.