As I stated before, anti virus, firewall, and spyware and adware programs are a must for todays computer with all that is out there on the Internet. The good news is that if you don't have the money to buy all of these programs, there are alternatives out there to download for free.
If you go with the paid programs, you can be more secure and will have many more options in most cases. Most paid programs use real time monitoring, meaning they try to stop the bad program from ever entering your computer. The free versions usually don't offer any real time monitoring and are just scanners to find bad programs after they are already installed. I currently run a variety of paid and free programs and I have no issues with viruses and spyware.
A major problem that we see when out doing repair work on most desktops and laptops in Phoenix, Arizona today is that most people think that they have adequate security against viruses and spyware, but they either have scanners from non-reputable sources, or they don't have a variety of scanners. As far as the anti virus and firewall, with these you only want one program. It's the spyware and adware programs, that I like to have more than one of. The problem with most peoples anti virus and firewall programs is that usually they got the programs with the computer when they got it, and those programs are trial programs that end in 30 to 90 days. It is essential in virus and spyware programs to have fully up to date information. Most of these programs find problems by having a built-in list to tell them what to look for. If there is a newer threat out there, and you haven't updated your programs to recognize it, you will be vulnerable. I like to have more than one spyware scanner. I have about 4 or 5 of programs, all from good companies, and one always gets something that the other one missed. This is why I believe that no computer is completely free of spyware, there is just too much of it, and too many people putting it out there in everything you do online.
I hope that while you are reading this, that you don't think, "I'm not going online now", or that you think twice before paying that bill online. I've been paying all of my bills online for years now, and I've never had an issue. I read recently that the head of Bank of America's online division said that the online division has less fraud than the actual bank locations do. It's all about being up to date. Most programs, even windows, you can set to auto update so they will keep up to date on their own. You just have to remember to watch when programs expire if they are a paid program to avoid computer repair issues.