I have a WD Passport HD and received the following email from them today:
Dear WD Registered Customer,
UPDATE: November 1st, 2013
As a valued WD customer we want to make you aware of new reports of Western Digital and other external HDD products experiencing data loss when updating to Apple's OS X Mavericks (10.9). WD is urgently investigating these reports and the possible connection to the WD Drive Manager, WD Raid Manager and WD SmartWare software applications. Until the issue is understood and the cause identified, WD strongly urges our customers to uninstall these software applications before updating to OS X Mavericks (10.9), or delay upgrading. If you have already upgraded to Mavericks, WD recommends that you remove these applications and restart your computer. If you have already upgraded to Mavericks and are experiencing difficulty in accessing your external hard drive, please do not save anything to the drive, disconnect the drive from your computer, and contact Western Digital Customer Service at http://support.wd.com/country/
for further assistance.
The WD Drive Manager, WD Raid Manager, and WD SmartWare software applications are not new and have been available from WD for many years. However, solely as a precaution WD has removed these applications from our website as we investigate this issue.