Many z/OS® systems are troubled by cases of message flooding, where a user program or a z/OS process itself issues a large number of messages to the z/OS consoles in a short time. For example, a user program might enter an unintentional loop that includes a WTO call, with the result that a potentially infinite number of messages are issued in a short time. Cases of hundreds (or even thousands) of messages a second are not uncommon.

The messages in a message flood are often similar or identical, but are not necessarily so. Techniques to identify similar messages can be difficult and time consuming.