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Anomaly detection aims at identifying unexpected fluctuations in the expected behavior of a given system. It is acknowledged as a reliable answer to the identification of zero-day attacks to such extent, several ML algorithms that suit for…

Machine Learning · Computer Science 2020-12-22 Tommaso Zoppi , Andrea ceccarelli , Tommaso Capecchi , Andrea Bondavalli

Isolation Forest (iForest) stands out as a widely-used unsupervised anomaly detector, primarily owing to its remarkable runtime efficiency and superior performance in large-scale tasks. Despite its widespread adoption, a theoretical…

Machine Learning · Computer Science 2026-01-28 Qin-Cheng Zheng , Shao-Qun Zhang , Shen-Huan Lyu , Yuan Jiang , Zhi-Hua Zhou

The anomaly detection literature is abundant with offline methods, which require repeated access to data in memory, and impose impractical assumptions when applied to a streaming context. Existing online anomaly detection methods also…

Machine Learning · Computer Science 2025-05-16 Filippo Leveni , Guilherme Weigert Cassales , Bernhard Pfahringer , Albert Bifet , Giacomo Boracchi

Anomaly detection is critical in various fields, including intrusion detection, health monitoring, fault diagnosis, and sensor network event detection. The isolation forest (or iForest) approach is a well-known technique for detecting…

Machine Learning · Computer Science 2021-10-06 Seemandhar Jain , Prarthi Jain , Abhishek Srivastava

Anomaly Detection (AD) is evolving through algorithms capable of identifying outliers in complex datasets. The Isolation Forest (IF), a pivotal AD technique, exhibits adaptability limitations and biases. This paper introduces the…

Machine Learning · Computer Science 2025-11-11 Alessio Arcudi , Alessandro Ferreri , Francesco Borsatti , Gian Antonio Susto

We present a novel strategy for detecting global outliers in a federated learning setting, targeting in particular cross-silo scenarios. Our approach involves the use of two servers and the transmission of masked local data from clients to…

Machine Learning · Computer Science 2024-09-23 Daniele Malpetti , Laura Azzimonti

Federated learning (FL), with the growing IoT and edge computing, is seen as a promising solution for applications that are latency- and privacy-aware. However, due to the widespread dispersion of data across many clients, it is challenging…

Machine Learning · Computer Science 2024-11-05 Dipanwita Thakur , Antonella Guzzo , Giancarlo Fortino

Isolation forest (iForest) has been emerging as arguably the most popular anomaly detector in recent years due to its general effectiveness across different benchmarks and strong scalability. Nevertheless, its linear axis-parallel isolation…

Machine Learning · Computer Science 2023-06-12 Hongzuo Xu , Guansong Pang , Yijie Wang , Yongjun Wang

Unsupervised anomaly detection tackles the problem of finding anomalies inside datasets without the labels availability; since data tagging is typically hard or expensive to obtain, such approaches have seen huge applicability in recent…

Machine Learning · Computer Science 2021-12-01 Tommaso Barbariol , Gian Antonio Susto

Anomaly detection plays an increasingly important role in various fields for critical tasks such as intrusion detection in cybersecurity, financial risk detection, and human health monitoring. A variety of anomaly detection methods have…

Machine Learning · Computer Science 2023-06-26 Haolong Xiang , Xuyun Zhang , Hongsheng Hu , Lianyong Qi , Wanchun Dou , Mark Dras , Amin Beheshti , Xiaolong Xu

Isolation forest or "iForest" is an intuitive and widely used algorithm for anomaly detection that follows a simple yet effective idea: in a given data distribution, if a threshold (split point) is selected uniformly at random within the…

Machine Learning · Statistics 2021-12-07 David Cortes

Isolation Forest (iForest) is an unsupervised anomaly detection algorithm designed to effectively detect anomalies under the assumption that anomalies are ``few and different." Various studies have aimed to enhance iForest, but the…

Machine Learning · Computer Science 2025-03-18 Hun Kang , Kyoungok Kim

Anomaly detection is the practice of identifying items or events that do not conform to an expected behavior or do not correlate with other items in a dataset. It has previously been applied to areas such as intrusion detection, system…

Networking and Internet Architecture · Computer Science 2018-01-31 James Zhang , Ilija Vukotic , Robert Gardner

We present an extension to the model-free anomaly detection algorithm, Isolation Forest. This extension, named Extended Isolation Forest (EIF), resolves issues with assignment of anomaly score to given data points. We motivate the problem…

Machine Learning · Computer Science 2020-07-09 Sahand Hariri , Matias Carrasco Kind , Robert J. Brunner

The widespread integration of new technologies in low-voltage distribution networks on the consumer side creates the need for distribution system operators to perform advanced real-time calculations to estimate network conditions. In recent…

Systems and Control · Electrical Eng. & Systems 2025-04-28 Petar Labura , Tomislav Antic , Tomislav Capuder

Internet-of-things (IoT) devices are vulnerable to malicious operations by attackers, which can cause physical and economic harm to users; therefore, we previously proposed a sequence-based method that modeled user behavior as sequences of…

Cryptography and Security · Computer Science 2021-09-30 Masaaki Yamauchi , Masahiro Tanaka , Yuichi Ohsita , Masayuki Murata , Kensuke Ueda , Yoshiaki Kato

The rapid expansion of Internet of Things (IoT) deployments across diverse sectors has significantly enhanced operational efficiency, yet concurrently elevated cybersecurity vulnerabilities due to increased exposure to cyber threats. Given…

Machine Learning · Computer Science 2025-12-01 Md. Sad Abdullah Sami , Mushfiquzzaman Abid

Web services are software systems designed for supporting interoperable dynamic cross-enterprise interactions. The result of attacks to Web services can be catastrophic and causing the disclosure of enterprises' confidential data. As new…

Cryptography and Security · Computer Science 2016-05-23 Reyhaneh Ghassem Esfahani , Mohammad Abadollahi Azgomi , Reza Fathi

In a context of a continuous digitalisation of processes, organisations must deal with the challenge of detecting anomalies that can reveal suspicious activities upon an increasing volume of data. To pursue this goal, audit engagements are…

Computational Engineering, Finance, and Science · Computer Science 2024-05-24 A. Herreros-Martínez , R. Magdalena-Benedicto , J. Vila-Francés , A. J. Serrano-López , S. Pérez-Díaz

In this paper, the mathematical analysis of the Isolation Random Forest Method (IRF Method) for anomaly detection is presented. We show that the IRF space can be endowed with a probability induced by the Isolation Tree algorithm (iTree). In…

Methodology · Statistics 2022-05-05 Fernando A. Morales , Jorge M. Ramírez , Edgar A. Ramos