Rocketfuel processes over 120 billion ad auctions per day and needs to detect fraud in real time to prevent losses. They developed Helios, which ingests event data from Kafka and HDFS into Storm in real time, joins the streams in HBase, then runs MapReduce jobs hourly to populate an OLAP cube for analyzing feature vectors and detecting fraud patterns. This architecture on Hadoop allows them to easily scale real-time processing and experiment with different configurations to quickly react to fraud.