100's of security event logs per second

I have a number of XP machines that just started logging litteraly hundreds
of successful logs to the Security log every second. Needless to say, the
logs fill up daily. The same Event ID's repeat, 560, 562 and 567. I
understand these are somewhat normal, but not at that quantity. I've scanned
for viruses, nothing. Has anyone seen this before, or have any
ideas/suggestions to fix this?

Thanks,
seh