Those who rely on Dropbox to store their personal files may have lost some of their data. The service has experienced some issues regarding a bug in older versions of its available desktop apps. This bug deleted files uploaded by affected users who activated the Selective Sync feature, leading some to find they'd lost a large amount of files.
Should users shut down (or restart) the affected clients while Selective Sync was active, they would find the feature not being able to locate a portion of the files uploaded to the cloud. The good news is Dropbox has been busy working to restore files where possible and releasing updated versions of the desktop apps. Dropbox has also implemented some extra safeguards to help prevent this kind of mass deletion from occurring once again in the future.
Let us know if you've been affected in the comments. Also, do you rely solely on cloud-based services for backing up files?