TripleFact: Defending Data Contamination in the Evaluation of LLM-driven Fake News Detection

Cheng Xu, Nan Yan

Abstract: The proliferation of large language models (LLMs) has introduced unprecedented challenges in fake news detection due to benchmark data contamination (BDC), where evaluation benchmarks are inadvertently memorized during the pre-training, leading to the inflated performance metrics. Traditional evaluation paradigms, reliant on static datasets and closed-world assumptions, fail to account the BDC risk in large-scale pre-training of current LLMs. This paper introduces TripleFact, a novel evaluation framework for fake news detection task, which designed to mitigate BDC risk while prioritizing real-world applicability. TripleFact integrates three components: (1) Human-Adversarial Preference Testing (HAPT) to assess robustness against human-crafted misinformation, (2) Real-Time Web Agent with Asynchronous Validation (RTW-AV) to evaluate temporal generalization using dynamically sourced claims, and (3) Entity-Controlled Virtual Environment (ECVE) to eliminate entity-specific biases. Through experiments on 17 state-of-the-art LLMs, including GPT, LLaMA, and DeepSeek variants, TripleFact demonstrates superior contamination resistance compared to traditional benchmarks. Results reveal that BDC artificially inflates performance by up to 23% in conventional evaluations, while TripleFact Score (TFS) remain stable within 4% absolute error under controlled contamination. The framework’s ability to disentangle genuine detection capabilities from memorization artifacts underscores its potential as a fake news detection benchmark for the LLM era.