Authors CurseForge

http://www.wowace.com/addons/charprivacy/

Update:
Important Note:
The current Blizzard implementation has a critical design error: The "Display Only Character Achievements to Others" options does not include the pets and mounts section, which means that it's possible to create an unique account-fingerprint with this 2 datasets! This means also that this addon is useless because of this Blizzard bug. This also means that you can do nothing to avoid an account-fingerprint and so everybody can see all characters from an account (level 10+).

-- -------------------------------------------------------------------------- --
-- CharPrivacy by kunda                                                       --
-- -------------------------------------------------------------------------- --
--                                                                            --
-- With Mists of Pandaria it's possible to get all characters from an account --
-- via 'data-mining' the armory using the 'Community Platform API'.           --
-- This is possible by matching account-wide achievements (which can produce  --
-- a unique account-fingerprint) between different character-datasets.        --
-- Prior Mists of Pandaria this was NOT possible!                             --
--                                                                            --
-- Blizzard added an option to disable such 'data-mining'-actions, BUT this   --
-- option is DISABLED by DEFAULT.                                             --
-- You need to ENABLE "Display Only Character Achievements to Others" with    --
-- each character (Interface -> Game -> Display).                             --
--                                                                            --
-- This addon simply checks if you have enabled this option. If this option   --
-- is disabled this addon automatically enables it and shows a message in     --
-- chat.                                                                      --
--                                                                            --
-- Blizzard MUST ENABLE this option by DEFAULT, or better:                    --
-- change logic, change text and make a real OPT-IN feature.                  --
--                                                                            --
-- -------------------------------------------------------------------------- --

Download:
http://www.wowace.com/addons/charprivacy/files/

I was going to write exactly the same addon. Guess I don't have to do it now. :p

On a side note, "data-determining" should probably be "data-mining". I guess the former is technically accurate, but the latter is the usual term for it in English.

Edit: Added translations for esES, esMX, frFR, itIT, ptBR, ruRU in r5. Russian probably reads like a two-year old wrote it, but I guess it's better than nothing. Can't do Korean or Chinese though, sorry.

Well, I tried to mix "data-mining" (collect information) and "determine" (find relations between information)...but you are right.

Kunda, never mind mounts and pets. Your account activity and achievements/achievement history will also appear on all characters and there's nothing you can do to avoid it. I filed a complaint with Blizzard but heaven only knows how long it's going to take, if they even bother to fix it at all. "It's not a bug, it's a feature," the latest way an unscrupulous programmer expects to be able to ram a sequoia tree up your rear-end and demand you thank them for it.

I know I'm going to regret asking this, but, what can people do with this account fingerprint when they have it? And can just any Tom, Dick or Harry among the player population get the tools to acquire this fingerprint?

i still am annoyed by the disregard for privacy that blizzard uses, this was a great addon for reminding me to turn the option on (or off?)...

Phanx, is there any way you would be interested in resurrecting this abandoned addon? it's nice to know you were also thinking about this situation. it seems to be working just fine, but i just thought it might be nice to see this on the "big" addon sites for others to see that there is an addon to help get around, or at least remind one to do so.

sorry for the necro, but i just couldn't find anything about this anywhere else for the most part, since the project is now abandoned.

thanks for your consideration Phanx - i love your addons!

Ordinarily my answer would be "it works fine, and I'm not going to take over someone else's project unless it's actually broken" but since the option in question doesn't actually do anything (see the first post in this thread) there wouldn't really be any point even if the addon was broken.

Blizzard just has no regard for player privacy, and that's that. Anyone who wants to can identify all the characters on your account using mount/pet data, or build a comprehensive picture of when you play by looking at the real-time activity data, and there's nothing you can do about it. :(