We irregularly check the list of newly registered customers.
This is done to delete spam-accounts and hacking-attempts created by bots.
Introducing the Captcha helped a lot here but it’s not perfect.
We noticed that the newest account listed for us was quite old.
Investigation
Some investigation found that a daily reindex process was stuck since October and the list of all account shown to us in the backend (and only that list) was not updated because a previous run of that had died but never released it’s database lock.
Luckily only the index of the user-list was affected. All other indices (like all products, all new products, all products with a price change,…) worked just fine.
…work never stops.
result
A short search revealed how we could get this unstuck.
Only the list of all user account for administration and customer support was affected.
Customers could create and use their accounts all this time with no issues.
In the end we found just 48 new accounts obviously created by bots.
(Before introducing the Captcha this number ranked in the tens of thousands.)