From an email I received this morning:
We are writing to inform you of changes to our website. Unfortunately, last Friday our webhost company deleted from their servers the entire files of several websites, including the Delphi Classics store. This was an error which we had no control over. We have managed to salvage web page information, eBook files and other data, but all customer accounts and order details were lost. The server on which we stored the backups was also affected, losing the details of thousands of orders and accounts.
We have been working hard over the last five days to build a completely new website, with improved performance and features, as well as a more secure location. Sadly, we are simply unable to restore your previous account details and you will need to create a new account to make a new order. When registering a new account, you can re-use the same username and password if you would like.
I'm not sure how something like this happens, but there you are.