During an audit of a multinational bank's disposal process, an IS auditor should be most concerned about backup media being disposed before the end of the retention period. This is because backup media contain sensitive and critical data that may be required for business continuity, legal compliance, or forensic purposes.
Disposing backup media prematurely may result in data loss, unavailability, or corruption, which may have severe consequences for the bank's reputation, operations, and security. Backup media not being reviewed before disposal, degaussing being used instead of physical shredding, and hardware not being destroyed by a certified vendor are also findings that may pose some risks to the bank's disposal process, but they are not as critical as backup media being disposed before the end of the retention period. References: ISACA CISA Review Manual 27th Edition, page 302.