What is the most significant concern for an IS auditor reviewing the compliance of installed software within an organization?

The most significant concern for an IS auditor reviewing the compliance of installed software within an organization is the presence of software that is not listed in the approved standards document. This is critical because approved standards documents outline the organization's policies and guidelines regarding the use of software. If software is not included in this document, it raises questions about its legitimacy, security, and compliance with organizational policies.

Using unapproved software can pose various risks, such as unauthorized access to sensitive data, unregulated software updates, and lack of technical support. Furthermore, it could expose the organization to legal liabilities if the software is found to infringe on licensing agreements or regulatory requirements. Therefore, ensuring that all installed software is aligned with an approved standards document is vital for maintaining an organization's overall compliance posture and risk management strategy.

While other factors such as documentation of software, user training, and license expiration are relevant, they do not usually carry the same level of immediate risk or impact on compliance as the absence of software from the approved standards.