Positive Technologies has published a detailed technical overview of the anomaly detection engine inside PT AF Cloud, its cloud-hosted web application firewall. The system processes tens of millions of WAF events daily and reduces them to an average of one notification per client per week, highlighting moments when the character of attacks against a tenant changes noticeably.
Traditional volume-based thresholds frequently miss attacks that begin during periods of declining legitimate traffic or that introduce new attack vectors without dramatically increasing total event counts. PT AF Cloud therefore constructs a profile for every tenant consisting of the proportional distribution of triggered protection rules. These profiles are compared against a weighted historical baseline using Jensen-Shannon distance, a symmetric measure bounded between 0 and 1 that remains finite even when a previously unseen rule appears.
Two parallel detectors run on different time scales. The hourly detector uses a short baseline of several hours to surface rapid changes such as the sudden appearance of SQL-injection or directory-traversal rules with hundreds of distinct payloads. The daily detector compares 24-hour profiles against several preceding days and catches slower shifts that never dominate any single hour. Both detectors combine an absolute distance threshold with a tenant-specific z-score to avoid flooding noisy or low-volume tenants with alerts.
When an anomaly is confirmed, the service automatically prepares an email containing the percentage change in event volume, the top five rules for both the current and baseline periods, the count of unique attack vectors, and direct links into the PT AF web interface filtered to the relevant time window. Analysis of 519 alerts sent over two weeks showed that 69 percent corresponded to either an active attack or a protection rule firing on legitimate traffic after an application change.
Internally, events are exported from PT AF Cloud into a Security Lakehouse where Apache Airflow orchestrates hourly profile recalculation and anomaly scoring. Separate delivery tasks ensure that transient notification-service outages do not cause duplicate messages.


