With the development of "cloud" computing technology, data can now be stored and synchronized online. In this way, the data is safe and very convenient because of its portability. Users can manage, view, download, or share with others from anywhere in the world. Some popular online data storage and sharing services today are Google Drive, Onedrive, Youtube, Dropbox, Copy, Mediafire and others.

The table below briefly introduces some cloud storage systems (Zenuni, 2014).

Zenuni, X., Ajdari, J., Ismaili, F., & Raufi, B. (2014). Cloud storage providers: A comparison review and evaluation. In Proceedings of the 15th International Conference on Computer Systems and Technologies (pp. 272-277).