The application of message-passing Graph Neural Networks has been a breakthrough for important network science problems. However, the competitive performance often relies on using handcrafted structural features as inputs, which increases computational cost and introduces bias into the otherwise purely data-driven network representations. Here, we eliminate the need for handcrafted features by introducing an attention mechanism and utilizing message-iteration profiles, in addition to an effective algorithmic approach to generate a structurally diverse training set of small synthetic networks. Thereby, we build an expressive message-passing framework and use it to efficiently solve the NP-hard problem of Network Dismantling, virtually equivalent to vital node identification, with significant real-world applications. Trained solely on diversified synthetic networks, our proposed model—MIND: Message Iteration Network Dismantler—generalizes to large, unseen real networks with millions of nodes, outperforming state-of-the-art network dismantling methods. Increased efficiency and generalizability of the proposed model can be leveraged beyond dismantling in a range of complex network problems.

Reinforcement Learning (RL) is a powerful method for controlling dynamic systems, but its learning mechanism can lead to unpredictable actions that undermine the safety of critical systems. Here, we propose RL with Adaptive Regularization (RL-AR), an algorithm that enables safe RL exploration by combining the RL policy with a policy regularizer that hard-codes the safety constraints. RL-AR performs policy combination via a "focus module," which determines the appropriate combination depending on the state—relying more on the safe policy regularizer for less-exploited states while allowing unbiased convergence for well-exploited states. In a series of critical control applications, we demonstrate that RL-AR not only ensures safety during training but also achieves a return competitive with the standards of model-free RL that disregards safety.

Graph Neural Network (GNN) is the state-of-the-art machine learning model on graph data, which many modern big data applications rely on. However, GNN’s potential leakage of sensitive graph node relationships (i.e., links) could cause severe user privacy infringements. An attacker might infer the sensitive graph links from the posteriors of a GNN. Such attacks are named graph link inference attacks. While most existing research considers attack settings without malicious users, this work considers the setting where some malicious nodes are established by the attacker. This setting enables link inference without relying on the estimation of the number of links in the target graph, which significantly enhances the practicality of link inference attacks. This work further proposes centroid-guided graph poisoning (CGP). Without participating in the training process of the target model, CGP operates on links between malicious nodes to make the target model more vulnerable to graph link inference attacks. Experiment results in this work demonstrate that using less than 5% of malicious nodes, i.e. modifying approximately 0.25% of all links, CGP can increase the F-1 of graph link inference attacks by up to 4%.