What security risk is most pressing when a user takes a USB flash device with confidential files?

When a user takes a USB flash device that contains confidential files, the most pressing security risk involves confidentiality. This risk pertains to the potential unauthorized access to sensitive information if the device is lost or stolen.

Confidentiality is crucial because it ensures that sensitive information is not disclosed to users who are not authorized to view it. If a USB drive containing confidential data falls into the wrong hands, the information could be easily compromised, leading to data breaches, identity theft, or other serious security incidents. This highlights the importance of encrypting files on USB devices and implementing access controls to safeguard sensitive information.

In contrast, while availability concerns the accessibility of information when needed, and integrity focuses on maintaining the accuracy and trustworthiness of data, these factors are secondary in this particular scenario compared to the immediate risk that unauthorized parties could access confidential information. Non-repudiation deals with ensuring that a transaction cannot be denied after it has been performed, which is less relevant in the context of a USB device being taken out of a secure environment.