A user behavior activity detection method is provided in which network traffic relating to user behavior activities in a network is monitored. Data is stored representing network traffic within a plurality of time periods, each of the time periods serving as a transaction. Subsets of the network traffic in the transactions are identified as traffic suspected of relating to certain user behavior activities. The subsets of the network traffic in the transactions are assigned into one or more groups. A determination is made of one or more detection rules for each of the one or more groups based on identifying, for each of the groups, a number of user behavior activities common to each of the subsets of the network traffic. The one or more detection rules are used to monitor future network traffic in the network to detect occurrence of the certain user behavior activities.