Which of the following would be classified as an incident?

An incident is defined within the ITIL framework as an unplanned interruption to a service or a reduction in the quality of a service. In this context, the option that refers to a system crash affecting users aligns perfectly with that definition. A system crash indeed represents an unexpected failure that disrupts normal service delivery, thereby impacting users' ability to perform their tasks. This fits squarely within the incident management process, which aims to restore normal service operation as quickly as possible and minimize impact on the business.

The other options do not meet the criteria for an incident: A request for additional software pertains to a service request, which is a normal request for a specific service or information and does not disrupt existing services. A proposal for change in the configuration refers to a planned change, which is part of change management, not incident management. Periodic system maintenance is a scheduled activity intended to ensure services remain healthy and does not constitute an incident as it is pre-planned and does not result from unplanned disruptions.