Dropbox can be used to share folders and files with specific clients securely so they can only view and modify their own respective folders and files.
Setting up a new client folder
Log in to the Dropbox website at https://www.dropbox.com/login
On the home page, create a new client folder by selecting 'New folder' in the panel on the right hand side.
Enter the client name and enter, the folder will then appear in the list. Hover your mouse of the folder and click 'Share'.
Type in their email address and set their permission level (edit or view), then click on 'Share'.
They will then receive an email invitation.
** Please ensure you invite the correct client to the correct folder to ensure there is no cross client sharing of data. **