upd likely stands for "update" — possibly someone looking for an updated list of exposed wallet.dat files or an updated recovery tool.
A small altcoin exchange in Southeast Asia misconfigured its Nginx server. A directory listing revealed /backup/daemon/upd/ . Inside was wallet.dat.upd containing over 500 LTC (Litecoin). A white-hat hacker discovered it via indexofwalletdat upd and notified the owner after moving the file offline.