I think the only problem with ZoneAlarm Pro (the normal version is a little crappy, it doesn't have much functions, but when it's free, hehe, it's not as good as when you pay ) is that it takes a really long time to load at startup with windows and is not fully compatible with windows XP (sometimes there are bugs, like bad performances, or even crashes, but it doesn't happen often). But ZoneAlarm Pro has been tested many times by lots of magazines, websites, and so on. And it appears to be the best to block outside intrusions and hackers. For example mine, who is installed on my computer, has blocked since install 56847 intrusions So it can't be bad I really would suggest you to take the free version if you don't want to pay, the other free firewalls are not as efficient as ZoneAlarm. Really.