Certain example embodiments described herein relate to systems and/or methods for event stream deviation detection. More particularly, certain example embodiments described herein relate to maintaining short and long-term statistics of an incoming stream of event data. In certain example embodiments, a deviation is calculated based at least in part on the long-term and short-term statistics. The deviation may then be compared to a threshold value. In certain example embodiments, the estimations required for the statistics are done with Kernel Density Estimators (KDEs).