Histogram-based Outlier Score (HBOS): A fast Unsupervised Anomaly Detection Algorithm

Unsupervised anomaly detection is the process of nding outliers in data sets without prior training. In this paper, a histogrambased outlier detection (HBOS) algorithm is presented, which scores records in linear time. It assumes independence of the features making it much faster than multivariate approaches at the cost of less precision. A comparative evaluation on three UCI data sets and 10 standard algorithms show, that it can detect global outliers as reliable as state-of-theart algorithms, but it performs poor on local outlier problems. HBOS is in our experiments up to 5 times faster than clustering based algorithms and up to 7 times faster than nearest-neighbor based methods.