There is no, and never has been, full security for Word. Corruption of documents has been an issue from the very beginning. That said, most corruption comes from improper opening and saving of the file.

Do not open and work on documents from email; always save the file to the harddrive and open it from there.

Do not open and work on files directly from a USB device; always save the file to the harddrive and open it from there.

Corruption can happen with really large documents, but the fact is most corruption stems from shaky file handling.

But yes, the bottom line is there are no warranties.