Flutterby™! :

As we're about to get hit hard by the "Oh, isn't it great that the serial numbers in Microsoft Word documents let us track down the creators" propaganda, it'll help your bullshit detectors if you remember that those numbers are only inserted when the document is created, not when it's edited. So if I open one of your documents and insert the virus, you're hosed. Similarly, all these mutations will point to one person.