I've used AVG, Avast!, and Antivir. All of them are free and scan every file as it is accessed. Is that not an "active" program? No one should have to pay money for a decent AV program. Pay versions tend to have a AV scanner surrounded by bloatware.
Well, it seems to be more specific it's REQUIRED.
I don't recommend Kaspersky in a general way; what I reccomend is Kaspersky Internet Security (also known as KIS); it costs just a little bit more of Kaspersky Antivirus (also known as KAV) but is a totally different software. KAV is a very good one, but is just an AV, that today is simply just NOT ENOUGH.
KIS is an INTEGRATED SECURITY SUITE with a lot of different real-time protection modules, very useful extra tools and features such as Safe Run for Websites, Safe Run for Applications, Vulnerability scanner based on Secunia database, Virtual Keyboard Anti-Keylogger (everything is typed from there can not be "seen" from the OS, it doesn't matter which kind of malware could be resident in), Program Control (HIPS), System Watcher and many more....
Besides, one of KIS componet is probably THE BEST firewall at the moment available: very powerful and highly configurable.
I can assure you there is NOTHING you can get for free that can be compared with KIS . More, mostly (if not ALL) of other shareware Security Suite can not be compared with KIS as well. But the main point, in my opinion, is that you don't know really what you are talking about (no offense, a lot of people don't get the right info about these kind of issue). What I can say to you is this: remove your free AV (AVG, Avast or Avira, you can reinstall it at any time, of course), download and install the trial version of Kaspersky Internet Security 2012 (it's free for 30 days with FULL functionality). There are also available instructions in PDF format.
Just try it, and you will see what I'm talking about. I hope everything is OK, but could be that your first "discover" will be that your PC is infected, and till now you don't know.