I run a small computer repair service. I am seeing this same problem with older single core XP SP3 systems, on boot up with Malwarebytes Pro v 1.75.0.1300. CPU goes to 100% and system is effectively locked up for 10+ minutes. This is with website blocking enabled. So far this is happening on two different customer's machines and only started with this new version of Malwarebytes. To test this on the one machine I took the hard drive and did a full format on it, reinstalled XP SP3, put on all the MS updates, loaded Office PRO 2003, MSE. System runs just fine but then load Malwarebytes PRO and whammo...BIG problem on rebooting. Nothing else loaded. It is mbamservices.exe that is chewing up the CPU resource according to Taskmanager. Eventually mbamservices drops back down to a normal cpu load and stuff starts working again. The free version does not have the problem. Until this gets fixed I can no longer recommend using the PRO version (and it was my favorite recommendation.