Parallels is warning users of its virtualization software not to upgrade their Windows environments to Windows 8 just yet, as the company has discovered that upgrading could lead to the loss of Windows data, files, and installed applications. The company just released a critical service advisory telling users not to upgrade until it finishes "testing the upgrade process" — it was unable to fully test the upgrade until now. This news is rather ill-timed, given that Microsoft's latest OS is ready to launch tomorrow; it's also a little odd considering Parallels released a major update this summer with complete Windows 8 integration. Still, virtualized environments for alternative operating systems can certainly be a bit tricky, so we're not going to ding Parallels too hard here.

The company also notes that you can install Windows 8 in a brand-new virtualized machine without an issue, so that's probably the best way to go if you just can't wait (or if you're a new user). Otherwise, you're best off waiting until Parallels completes its testing — being the first on the block to install Windows 8 on your Mac isn't worth it if you could lose data in the process. An in-product notification will let you know when it's safe to proceed.

Update: Parallels sent us a statement regarding the issue:

Parallels issued the service advisory below in advance of Friday’s Windows 8 availability to ensure our Parallels Desktop for Mac customers were aware that while full installations of Windows 8 previews and RTM builds have been successfully tested, as well as downloaded and installed by hundreds of thousands of customers, the Windows 8 upgrade is not available for testing until Friday. It is important for customers to know the potential dangers of installing the Windows 8 upgrade in their virtual machine until we can test it to confirm there are no known issues. When Windows 8 upgrade is available Parallels will immediately run tests and update our customers regarding the outcome as soon as possible.

In the meantime, we encourage everyone who is eager to try Windows 8 to install the full version of Windows 8 to experience exciting new operating system. Parallels Desktop 8 for Mac customers can also enjoy and choose the amount of integration between Mountain Lion and Windows 8 that best suits them.