AI can now identify anonymous internet users with 68% accuracy and 90% precision, effectively ending the “practical obscurity” that pseudonymous accounts have relied on for decades. A study covered by Hacker News shows that large language models like Gemini and ChatGPT can unmask anonymous posters in minutes, a task that would take human investigators hours, if they could pull it off at all.
The research, led by Daniel Paleka from ETH Zurich, compared LLM-based de-anonymization against traditional methods. The gap is staggering.
📊 The Numbers
- 68% of anonymous users identified correctly
- 90% precision on those identifications
- Near 0% success rate for the best non-LLM method
- Models completed in minutes what takes humans hours
What the Researchers Did
The team collected thousands of posts from anonymous forums, including Hacker News and Reddit. They chose accounts where they could verify real identities, like Hacker News profiles linked to LinkedIn accounts. They anonymized the data, then fed it to language models with prompts asking them to match users based on overlapping traits: location, profession, hobbies, demographics, and values.
The AI didn’t just find information users explicitly shared. It pieced together subtle clues scattered across years of posting. One example profile, reconstructed entirely from forum comments:
“She lives in Nelson, British Columbia. Pediatric nurse. Married, two daughters. Owns a Prius. Obsessed with sourdough. Plays Stardew Valley. Fan of Critical Role. Supports nuclear energy. Celiac. Plays the mandolin. Walked the Pacific Crest Trail end to end. Does not like cilantro.”
Even less obvious signals showed up. Visiting the Berlin subreddit. Using British spelling. Accidentally typing a “¿” in English text. Each detail alone is harmless. Together, they paint a portrait.
Why This Matters Right Now
This isn’t just an academic exercise. The practical implications are already playing out in real disputes.
Anthropic and the Pentagon are in a legal battle partly over this exact capability. In its statement to the Department of Defense, Anthropic warned: “Powerful AI makes it possible to assemble this scattered, individually innocuous data into a comprehensive picture of any person’s life, automatically and at massive scale.”
The concern goes beyond identifying someone. As Paleka puts it: “The existence of a mechanism to investigate or monitor with large language models that allows us to simply ask about a person’s beliefs, political opinions, insecurities, or anything else that can be extracted from their anonymous Reddit account could disempower many people today.”
You don’t even need to dox someone. Just knowing what AI can reveal about a pseudonymous account changes the power dynamic.
What’s Still Safe (For Now)
“I don’t believe that today, the models can reliably de-anonymize someone who is truly difficult to identify,” Paleka says. “Satoshi Nakamoto is safe. In the future, they could become better than people at this type of research, and then, the balance could shift.”
The researchers deliberately limited their database out of ethical concerns. They haven’t explored more aggressive de-anonymization approaches, though they acknowledge those would be straightforward.
What You Can Do With This Knowledge
- Assume everything you post is linkable. Treat pseudonymous accounts as thin privacy layers, not real protection.
- Separate concerns across accounts. The more biographical overlap between accounts, the easier AI can connect them.
- Watch for subtle leaks. Spelling patterns, subreddit visits, cultural references, and even punctuation habits all contribute to your digital fingerprint.
- Rethink old posts. Paleka’s advice is direct: “Keep in mind that everything you post stays on the internet and can become the target of future models” that will be even more effective.
What stands out here is the quantification. Many people suspected this was possible since LLMs gained search capabilities in 2023-2024. This study puts hard numbers on it, and those numbers should make anyone with a pseudonymous online presence reconsider what “anonymous” actually means today.
The full research details are available through the original source on Hacker News.