Cloud Storage meets our needs for more and convenient storage space.However, Nobody can 100% guarantee cloud storage safety.Password can be hacked. Data can be intercepted while it is traveling.For crucial reasons, data can be checked by some authorities.

During 2012, Dropbox has been attacked and with over 68m users’ email addresses and passwords leaking on to the internet. See more https://www.theguardian.com/technology/2016/aug/31/dropbox-hack-passwords-68m-data-breach.  Besides, Data can be captured en route and your data isn't always immune to search and seizure by local government entities. In the U.S., for example, any cloud storage company could be served a subpoena requiring them to open their clients' data for government examination. See more https://computer.howstuffworks.com/cloud-computing/files-safe-in-the-cloud.htm

It is good that most storage services will encrypt the data while it's traveling back and forth. However, it is even better that people guard data on their own by encrypting their data in advance to have double protection and to keep away from worries of cloud attacks.