Large language models (LLMs) like GPT-4 can identify a person's age, location, gender and income with up to 85 per cent accuracy simply by analysing their posts on social media. Robin Staab and Mark Vero at ETH Zurich in Switzerland got nine LLMs to pore through a database of Reddit posts and pick up identifying information in the way users wrote. Staab and Vero randomly selected 1500 profiles of users who engaged on the platform, then narrowed these down to 520 users for which they could confidently identify attributes like a person's place of birth, their income bracket, gender and location, either in their profiles or posts. When given the posting history of those users, some of the LLMs were able to identify many of these attributes with a high degree of accuracy. GPT-4 achieved the highest overall accuracy with 85 per cent, while LlaMA-2-7b, a comparatively low-powered LLM, was the least accurate model with 51 per cent. "It tells us that we give a lot of our personal information away on the internet without thinking about it," says Staab. "Many people would not assume that you can directly infer their age or their location from how they write, but LLMs are quite capable."