Imagine that you are a Dropbox user and regularly copy your important (and sensitive) files to your Dropbox account for backup purposes. Here's what Dropbox says about the security of your files:

Dropbox protects files in transit between our apps and our servers, and at rest. Each file is split into discrete blocks, which are encrypted using a strong cipher. Only blocks that have been modified are synced.

Can anyone read your files except you? Explain.