I just wanted to chime in here and officially add another person to the list that is having issues with the latest update. I also have win xp sp3, Avast 6 and Zone alarm. I use the paid version of malwarebytes. I am having the problem with my system completely locking up after I updated to 1.6.0.1800. I did submit a service ticket a few minutes ago. I have used the mbam-clean utility and rebooted, but that did not fix the issue for me. I have narrowed it down to the "enable protection module". If is it not checked, then mbam runs fine with Zone Alarm. As soon as it is checked, my system locks up. Hope the problem with ZA will be fixed soon or that you revert back to the older version of the protection module that did not have problems.