Final Fantasy 14: Dawntrail introduced a range of new blacklist features aimed at addressing complaints that the MMO did not offer enough tools to help people escape stalking and harassment from other players.
Unfortunately, it seems the implementation of these changes has introduced a backend exploit that could make it easier than ever for bad actors to harass, and mods are starting to emerge that take advantage of it.
With the introduction of the new blacklist features in Dawntrail, blacklisting an individual character would now block all characters tied to that player's account.
As PC Gamer notes, players soon discovered that, alongside this feature, each player now had a unique "account ID" that would be broadcast to the game client whenever you entered the same area as one of that player's characters.
With the right mod, somebody could, in theory, start matching characters to account IDs and build a database that makes public any given individual's full roster of alts.