If you made your game with Unity (maybe others too, not sure) and your name input field allows rich text, people can add tags such as <b>, <i>, <color=blue>, <size=500>, even <color=#0000> to make the text invisible. Even worse, if they don't close the tag the effect will be applied to the rest of the leaderboard text! This means <color=#0000> could make half of your leaderboard disappear.
I changed the Content Type of my text box to only allow alphanumeric characters to prevent this, and I recommend everyone do the same or find another solution before your leaderboards get messed up. You can also delete individual scores with LootLocker to remove already-messed-up entries. A limit to the length of a player's name would also help against super-long names.
