Federated learning provides an effective solution to the data privacy issue in distributed machine learning. However, distributed federated learning systems are inherently susceptible to data poisoning attacks and data heterogeneity. Under conditions of high data heterogeneity, the gradient conflict problem in federated learning becomes more pronounced, making traditional defense mechanisms against poisoning attacks less adaptable between scenarios with and without attacks. To address this challenge, we design a two-stage federated learning framework for defending against poisoning attacks—FedCVG. During implementation, FedCVG first removes malicious clients using a reputation-based clustering method, and then optimizes communication overhead through a virtual aggregation mechanism. Extensive experimental results show that, compared to other baseline methods, FedCVG improves average accuracy by 4.2% and reduces communication overhead by approximately 50% while defending against poisoning attacks.

As a distributed communication and storage system, blockchain forms a Computing Power Blockchain Network (CPBN) by integrating computing nodes and network resources. However, its open architecture faces major security threats such as Sybil attacks, computational fraud, and DDoS attacks. Traditional detection methods often fail in dynamic environments with scarce domain data. To address this, we developed a lightweight blockchain simulator to generate Sybil and DDoS attack scenarios, constructing a 14-dimensional feature dataset. To address Sybil attacks and distributed denial-of-service attack scenarios, this paper proposes an adaptive attention random forest convolutional neural network anomaly detection method (CAA-RF). Our approach uses multi-layer convolutional operations to capture high-order data correlations, combines attention mechanisms for global dependency modeling, and employs random forest for robust anomaly detection, enabling effective real-time security protection for blockchain systems.