Good looking out- your intentions were in the right direction!
I use Zone Alarm (free) for a fire wall, and a virus program called Avast! (free again!). The only time I ever got a virus was with Norton Antivirus 2002 running. It missed it completely
I also have Spybot Search and Destroy (free) for ridding tracking devices and spy ware. I've heard Ad-Aware contains (gasp!) SPYWARE included in the program!
Also, for windows users you would be amazed how much of an improvement your system can undergo if you reformat your hard drive and install windows clean once a year. It does take me a couple hours to update back everything and install all my programs, but I find it
very worth while.