Hard drive manufacturer Western Digital is warning users of the company’s external hard drives that there may be conflicts between OS X 10.9 Mavericks and the bundled utilities WD Drive Manager, WD Raid Manager, and WD SmartWare. These conflicts could case data loss, and until more is known, Western Digital recommends that users of these applications delay upgrading to Mavericks or delete the applications and restart. Thanks to reader Charlie Colosky for the alert!
The RoaringApps software compatibility site lists as being incompatible with Mavericks, with one commenter claiming that Mavericks identified it as incompatible during the upgrade. The  either lack Mavericks-specific information or aren’t listed with RoaringApps.
[Update: 6 November 2013: Western Digital has, saying that the problem is yet to be fixed, but affects only a small number of users. Western Digital urges customers running Mavericks to uninstall the Western Digital software (an  is available), reboot, and if there’s any difficulty accessing the drive, to disconnect it and contact customer support. The company says that lost data can likely be recovered with a data recovery utility.]