EVALUATING AND MODIFYING COUNTERMEASURES BASED ON AGGREGATE TRANSACTION STATUS

Techniques are provided for evaluating and modifying countermeasures based on aggregate transaction status. A first expression pattern is determined that occurs in each of first response messages served by the web server system in response to successful transactions of the transaction type. A second expression pattern is determined that occurs in each of second response messages served by the web server system in response to non-successful transactions of the transaction type requested. Aa status is determined for each of a plurality of transactions of the transaction type based on matching the first expression pattern or the second expression pattern to response messages served by the web server system. Aggregate status information for the transaction type based on the status for the set of operations is updated. Based on a change in the aggregate status information, a set of one or more security countermeasures is updated.