System "resaves" all files

I've got Vista 64 on my desktop - a HP that is little over a year old. When I go into Windows Exploer I like to organize files in a folder by date - chances are I am looking for something I was using recently. Well within the last few months the system has every once in a while "resaved" all files - Word, Excel, etc. to the same date and time. It most recently happened Jan 24 at 8:41 pm - so everything I have not saved since then reads that date and time. Can anyone tell me how to stop this from happening?
Thanks
Bill

Think about the first time that this happened. Did you install any new software? Were there any unique events that occurred? If the answer to any of these are yes, then that is the answer. But, I am pretty sure the answer is no. If that is the case next time that it happens go to the event viewer and find out what happened at that time.

As always, whenever there is an unexplained event, I would do an antivirus scan and and a scan with malwarebytes, which can be downloaded from their site.