Even though you are probably (hopefully!) in a good habit of backing up your essential data like payroll and accounting to an external hard drive, if you are running Mac’s new OS X Mavericks, DON’T! There have been hundreds of reports of the new operating system destroying data on external hard drives. It should be something that will be fixed with a patch, but no patch has been released yet.
Western Digital has come out with some good step-by-step instructions on how to safely access your external hard drive. Otherwise, sit tight!