ETH Zurich / Anthropic Paper: LLMs Unmask Pseudonymous Users for $4 Per Person at 67% Accuracy — 'Practical Obscurity No Longer Holds,' ICLR 2026 Workshop

r/ChatGPT / ETH Zurich / arXiv·high signal

Researchers from ETH Zurich and Anthropic published a paper at the ICLR 2026 Workshop demonstrating that LLM agents de-anonymize pseudonymous internet users for $1–4 per person, correctly identifying 226 of 338 targets at 90% precision across ~1,000 Hacker News profiles and ~10,000 Reddit users matched to real LinkedIn identities. The system exploits the same contextual writing signals a skilled investigator would use but automates the process at scale and near-zero cost. The authors conclude that 'practical obscurity' for pseudonymous accounts no longer provides meaningful protection and that online privacy threat models must be fundamentally reconsidered. Surfacing on r/ChatGPT today at 344 upvotes.