At a recent Literary Festival the writer of GCHQ (the uncensored version) explained that a US author had found that his book on the equivalent of GCHQ - the NSA in the USA had been fully accessed before publication by the NSA because he’d used the Cloud. The book was thereby open to being censored. In the UK the GCHQ book hit the shops before GCHQ heard about the publication.
It’s a point worth considering if you’re writing could be contentious. So Dropbox may not be the best place for your backups in some cases!!!