[Zope] How can I reset zope time???

Through a zwiki a spammer proxied some information though a zope server using zwiki's comments (be aware!). The spammer had dated his ip-packets 11/12-2007. And all my changes got the same date! So, I couldn't shrink all the undo actions though the database shrinker (later I found out that should just use -300). To get rid of 10 GB of undo history, I changed the computers time to 12/12-2007 and then undoed and gave the computer the right time again. Fine! But, now, not only have all my changes the date 12/12-2007 in the undo history, every object I have changed gets this date as well! Apparently, zope won't accept to go backward in time. How do I reset the zope's time? DateTime().Date() gives the right time. Flemming