Recently a vulnerability was posted to Bugtraq related to ZoneAlarm. The root problem is actually a Windows problem. ZoneAlarm is vulnerable because it runs on Windows, but not by any fault of Zone Labs or through any programming they are responsible for.
Zone Labs stated that they would not be patching ZoneAlarm (because the flaw isn't in their software) and pointed out that ZoneAlarm Pro had additional functionality that would protect users from this flaw. And so began the storm of misinformation.
Security news sites and message boards all over the world announced that Zone Labs was not providing maintenance for users of the free version and told everyone if they want support and updates they should buy the Pro version. Users everywhere flamed Zone Labs with venemous posts vowing never to use their products again.
After the press took the Zone Labs comments out of context and sensationalized them to spark fury in the user community (spin doctoring the statements as if they had an axe to grind with Zone Labs) Zone Labs eventually ate those words and agreed to release a patch to fix the flaw. The "patch" actually will just be an update adding the functionality from the Pro version that protects users from this Windows vulnerability.
Now, there are reports that upgrading from version 3.7 to 4.0 breaks some functionality without letting users know. There are certain firewall rules users may have configured in ZoneAlarm Pro 3.7. The documentation for Version 4.0 supposedly leads one to believe this functionality still works, but a statement from Zone Labs actually confirmed that some rules may have been removed due to lack of use.
Details are sketchy and not independently confirmed. You can read more about this at Security News Portal.
Given Zone Labs reputation of providing a quality firewall product I am inclined to give them the benefit of the doubt until proven otherwise. I certainly don't want to spark another round of misinformed controversy that forces Zone Labs to fix flaws that don't exist or take responsibility for vulnerabilities at the operating system level.
Often in cases like this one man's "flaw" is another man's "feature". If you have upgraded to ZoneAlarm 4.0 I suggest you do your own homework and research- or contact Zone Labs yourself and make up your own mind.