Word Files

I was backing up a users files on to the network to be transferred to a new computer. While copying them over, I was promtpted several times with "replace" file (only Word files) with newer/older version. Sometimes I answered yes/no, depending on which was newer. After the transfer, we could not locate any of the Word files, however everything else tranferred. I'm wondering if there was a virus that would cause this, or something else. I just looking for some insite as to what may have caused this. Thanks