sometime zone alarm conflicts with another program or just plain gets messed up and needs a reinstall (norton does the same so don't shoot the messenger) If you have any other antivirus (email attachment scanners) or firewall software (including microsofts default) then remove them because they won't run good together. In the case of antivirus, zone alarm scans mail and so does antivirus programs so shut down one or the other from scanning the mail so that only one does it.
Zone alarm has caused this problem intermittently over the past few years, it seems to conflict with some programmes more than others. Outlook in particular.
Sometimes it resolves itself.
Doing a complete uninstall and clean reinstall of the latest version usually fixes it for me.
Also clear internet cache and windows temp folder.
Run Spybot or Adaware and do an AV scan just to make sure.
Norton Internet Security has about 4 different componants and combined they use about 64MB of memory. I have seen several computers with ZoneAlarm having conflicts and misbehaving so it doesn't suprise me that there are wild differences from machine to machine. NIS has been known to have some issues at times also but in general I think NIS is the better choice even though I do like ZA, everytime I have an experience with it it seems to be messing up someones system.
I had this problem for a while too. I've found that 9 times out of 10, there's a version of the MSblast worm on your computer, and that causes vsmon.exe to take up a lot of cpu time.
Since Blast and blast variants all replicate themselves by accessing the internet, the firewall is involved. usually, these worms will try to access the internet through dllhost.exe or wintask2.exe or any number of others. The zone alarm window will pop up, asking if this application (i.e. wintask2.exe) may access the internet. if you say yes, which seems like a good idea because it sounds so legitimate, then your internet connection will be bogged down tremendously. If you say no, which you should, because there's no reason for this legitimate program to access the internet, then vsmon.exe will take up more and more cpu time trying to block all the attempts of this thing to access the internet and replicate itself.
Look in the logs of Zone alarm and find out which program is trying to access the internet really frequently (like 30 times a minute) and then look up the information on that application. Chances are you'll be directed to an antivirus site when you google for the name of that application (the one trying to access the internet very frequently) and then you can take steps to remove it.
This is not a problem with Zone Alarm, this is just the result of Zone Alarm doing it's job too well. ZA really is a great program.