Backup A backup is a copy of one or more files created as an alternate in case the original data is lost or becomes unusable. It’s not just hardware malfunctions, software corruption can also damage files. Directory structures can become damaged and cause entire folders to disappear. Files can be mistakenly deleted or corrupted by viruses or other software attacks. Program installation conflicts can make applications or files unusable. There are unfortunately many ways for your data to become damaged or disappear. That is why it is so important to backup data.