Xbox One Preview Testers, please take note that the latest and most recent dash download has a glitch that will factory reset your console and remove all of your games from the HDD. This bastard of an issue will have you seething with gritted teeth!
Microsoft has said in an official statement:
Due to an unforeseen issue with our update system, if when powering on your Xbox One console you are asked to download a system update, please decline it. By declining the update you will go off-line and not be factory reset. Please leave your console powered on until further notice.
We’ve identified an issue that could cause a small sub-set of consoles enrolled in Public Preview to factory reset after downloading the latest system update (deleting all local hard drive content). Note that a factory reset does not impact profile settings or game saves (which are synced to our servers when you connect to Xbox Live), or content stored on an external hard drive. For now, please decline the system update until we can address this issue on our end.
Please remember that declining the update will disconnect your Xbox One from Xbox LIVE and will not be able to play online. We do not yet know when a fixed update will be released, but I am sure MS will not hold back long!