Graph Anomaly Detection at Group Level: A Topology Pattern Enhanced Unsupervised Approach

TL;DR

This paper introduces an unsupervised framework for detecting anomalous groups in graphs by leveraging topology patterns and contrastive learning, addressing the gap in existing methods that focus only on individual nodes or graphs.

Contribution

It proposes a novel group-level graph anomaly detection framework combining a GAE-based anchor node locator and topology pattern-based contrastive learning for improved anomaly group identification.

Findings

Superior performance on real-world datasets

Effective localization of anomaly groups

Demonstrated robustness on synthetic data

Abstract

Graph anomaly detection (GAD) has achieved success and has been widely applied in various domains, such as fraud detection, cybersecurity, finance security, and biochemistry. However, existing graph anomaly detection algorithms focus on distinguishing individual entities (nodes or graphs) and overlook the possibility of anomalous groups within the graph. To address this limitation, this paper introduces a novel unsupervised framework for a new task called Group-level Graph Anomaly Detection (Gr-GAD). The proposed framework first employs a variant of Graph AutoEncoder (GAE) to locate anchor nodes that belong to potential anomaly groups by capturing long-range inconsistencies. Subsequently, group sampling is employed to sample candidate groups, which are then fed into the proposed Topology Pattern-based Graph Contrastive Learning (TPGCL) method. TPGCL utilizes the topology patterns of groups as clues to generate embeddings for each candidate group and thus distinct anomaly groups. The experimental results on both real-world and synthetic datasets demonstrate that the proposed framework shows superior performance in identifying and localizing anomaly groups, highlighting it as a promising solution for Gr-GAD. Datasets and codes of the proposed framework are at the github repository https://anonymous.4open.science/r/Topology-Pattern-Enhanced-Unsupervised-Group-level-Graph-Anomaly-Detection.