Even if your computer has a meltdown, your stuff is safe in Dropbox and can be restored in a snap. In fact, if you're using the Dropbox desktop application, your files are backed up several times. The primary copy on your computer's hard drive is synced to your Dropbox account online, and that copy is backed up again for safety. If you're using Dropbox to sync files between multiple computers, your files are backed up on those computers as well.
By default, Dropbox saves a history of all deleted and earlier versions of files for 30 days for all Dropbox accounts. If you purchase the extended version history add-on feature, you can revert to a previous file version or recover a deleted file at any time within a year of an edit or deletion made after your purchase.
All files stored online by Dropbox are encrypted and are kept in secure storage servers across several data centers.