We've been going over two years without any "anti virus" program running on our laptop. I've decided that there is very little possibility of having a virus problem, provided you use a little bit of common sense. I would certainly never pay for one, and I find that the free ones slow down my system.
First of all, never open an email attachment if you're not positive as to what that attachment contains.
Next, pay attention to what website you plan on visiting. If you are searching for something on google, pay attention to the web address before clicking on it. For example, never click on a site that contains too many numbers such as http://www.188.8.131.52/reservis.ru Notice also the ending of the web address...you will very rarely find what you're looking for at a site that is not .com, .ca, or .org.
The text displayed for the link does not have to be the real destination. For example, this link http://www.ottawasun.com/ really takes you to microsofts home page. There is no rule that says the displayed text has to be the real destination. Most of the time, hovering your cursor over a link in both an email program and a web browser will display the destination of the link in the status bar at the bottom of the screen. If it doesn't, you should be cautious. So that is something else you should always check.
If you are still unsure, Microsoft has finally come out with a totally free antivirus program that I've tested and I think it's not bad. You can get it here Microsoft Security Essentials
Regarding unsecured wi-fi connections, there are people who think they are not safe to use for banking or anything personal. This is simply not the case. If there were to be a problem, the person causing the problem would have to be a computer genius, a crook, and have access to very expensive and complicated computer hardware. Therefore, the odds of you encountering a problem are very, very, slim. So slim, it is not worth worrying about.