Hi megfl,
Well the answer to your question is not that easy, and depends on a variety of factors. The days that a simple anti-virus solution together with a software firewall could keep your computer free of malware are long gone. Now you need another attitude of computing and a layered defense to stay free of malware, you can read all about that here in this our forum, welcome to a treasure of knowledge.
You need anti-spyware programs like ad-aware, spybot s&d, spyware blaster, in-browser security, script blocking etc, free spyaudit scan now and again.
Just on the topic of anti-virus solutions there is a free solution, and that has kept my computer free of malware over the last couple of years: avast together with non-resident ClamWin (open source), in-browser DrWeb hyperlink pre-scanning plug-in, NoScript in the FF or Flock browser, MacAfeeSiteAdvisor, and additional online scanning with Bitdefender. Free DrWebCureIt from a mem stick. And for heuristical scanning the old free F-prot for Dos with automatic updater, and stinger.exe.
If you do want to pay money for it per-se, and you are not an advanced user, you could think about KAV (best virus update regime, DrWeb is second, but has more FP's), Nod32 is also advised by anti-malware forums.
One word of caution, rather not use the big three like Symantec, MacAfee or TrendMicro, because malware artists test their new creation against detection of these scanners, so for a zero day virus you are less protected there, with is
too big of a what we call "vulnerability window", the time between the risk of actual infection and protection is too big. Well that is what I know about this, there are others that hold other opinions, but this is my experience,
Well it is a fact that a lot of people will choose MS one-care solution, when it comes integrated with the OS, the same like it was when IE came in or with MS Media Player, "sheople" always eat what is placed in front of them, and what "the others" do. That also has been a big part of Microsoft's success over the previous years.
Enjoy your visits here, and stay malware free iin the future,
polonus