Is anyone experiencing an odd spam user attack? Any way to block?

Support
4

Yes, I had this too, and it stopped after I switched to manually approving posts for TL0 users.

I have a custom field that lets registering users select their operating system(s) (my community is for an app), and these bot accounts had random data in that field.

I used a custom Data Explorer query to list all users with an invalid operating system value, that is, a value not included in the predefined list of options for the custom user field.

SELECT 
  u.id, 
  u.username, 
  ucf.value AS user_field_1 
FROM 
  users AS u 
  LEFT JOIN user_custom_fields AS ucf ON u.id = ucf.user_id 
  AND ucf.name = 'user_field_1' 
WHERE 
  ucf.value IS NOT NULL 
  AND ucf.value NOT IN (
    SELECT 
      ufo.value 
    FROM 
      user_field_options AS ufo 
    WHERE 
      ufo.user_field_id = 1
  )