“…One of the most challenging problems in the field of intrusion detection is anomaly detection for discrete event logs. Researchers have been trying to resolve this challenge for two decades, and most work have focused on applying unsupervised learning upon engineered features from normal data, assuming unforeseen anomalies do not follow the learned normal patterns (e.g., [27], [33], [25], [35], [29], [38], [3], [36], [31], [32]). Recently, solving this challenge with deep learning has gained a substantial amount of traction in the security community (e.g., [15], [6], [17], [16], [47]), partially due to the unique advantages of deep learning in natural language processing.…”