The specific issue here seems to be that Anthropic allows the unrestricted upload of personal files to the anthropic cloud environment, but does not check to make sure that the cloud environment belongs to the user running the session.

This should be relatively simple to fix. But, that would not solve the million other ways a file can be sent to another computer, whether through the user opening a compromised .html document or .pdf file etc etc.

This fundamentally comes down to the issue that we are running intelligent agents that can be turned against us on personal data. In a way, it mirrors the AI Box problem: https://www.yudkowsky.net/singularity/aibox