"If we provide your Dropbox files to a law enforcement agency as set forth above, we will remove Dropbox's encryption from the files before providing them to law enforcement," read the new terms.

"Just so you know, we don't get very many of those requests -- about one a month over the past year for our more than 25 million users. That's fewer than one in a million accounts," the company said in a subsequent .

For users such as Soghoian, this renders the use of encryption moot. If the file is secure while it is encrypted, but that encryption can be removed at any time, in what sense is the file secure at all?

The core of the Dropbox controversy is that because it encrypts users' files, it necessarily stores the keys used to provide that security. In storing those keys, it has the capability to decrypt files. One solution -- recommended by Dropbox -- is for users to encrypt files before uploading them but this comes at a price. Users can synchronize files between desktop PCs and smartphones, for instance, but no longer open them without loading a dedicated utility which might or might not be available on that device.

The Dropbox response to this is that the service is not intended as a fully-secure file repository, merely as a service that is more secure than conventional ways of carrying around data such as on unencrypted USB sticks.