I have found a free antivirus solution all together. We currently use it at my school as alternative to our current paid solution (and it actually works better). You can get it from http://www.avast.com. It's the Avast Home Edition 4.1. All you have to do is register it and you will receive a 14 Month license. When it expires, you simply renew your registration. Real-time scanning is a feature. Check it out.