I have Zone Alarm, AdAware 6, Spybot Search and Destroy and Avast all installed. The only problem I've had is that Avast reports the reference and quarantined files for both of the Spyware scanners as containing viruses, when in fact it's just the reference files. All I did is add those folders into the Avast ignore list when doing a complete scan and that solved the problem. All three applications are free and are a must for anyone concerned with online security! You may also want to consider using an alternative to Internet Explorer. I've tried Opera and Mozilla Firefox and they work great and aren't a high profile target like Internet Explorer is. Don't go online without a Firewall! Good Luck!