Telemetry (opt in). From 1.2.7 the game asks once whether to share combat data. Nothing is sent unless you say yes. With sharing on, each monster fight adds one row of whole numbers with these values and no others: the outcome (victory, fled or death); your class, level, maximum HP, HP at the end of the fight, strength, dexterity, weapon power and armor power; the monster's family, level, maximum HP, strength and defence, and whether it was a boss; the number of monsters and the encounter size; who acted first; the dungeon floor and difficulty; whether you had teammates, the party size and teammates lost; rounds; total damage dealt and taken; damage to you by kind (basic, ability, spell, damage over time); damage to your team; damage by you and by your team; healing you received; potions, abilities and spells used; XP and gold gained. No player or monster names, no chat, no save contents, no hardware ids. Each upload also carries the game version, the kind of install (single player, Steam, BBS door or server) and a random id.
On single player and Steam the id is made when you say yes, covers every character on that copy of the game, and you can replace it under Preferences. On a BBS or self hosted server the id belongs to that server and is shared by its players; no player can replace it. The operator must allow sharing there, each player is still asked, and the answer is for that player's account.
The data is pseudonymous, not anonymous. Exact stat values can link one character's fights, even across a new id, and on a small BBS or server the rows can be told apart by anyone who knows it. Addresses are not stored with the rows. Rows are kept for up to 30 days, including rows sent before you turn sharing off. Turning it off deletes anything not yet sent.
Posted by the game’s developer or publisher to its Steam community hub and published by Valve through Steam’s public news API. Sifter reproduces it unedited and writes none of it.