Free version is free
And very good. A tech friend of mine turned me on to it when he helped me clean out a computer that had become majorly infected with multiple viruses. I've been using Avast ever since.
Also just like to say, Norton is more of a virus than an anti-virus in my opinion. It's not really any good. I don't recommend anyone using Norton (and I remove it from friends/family members computers when they speak of anti-virus)