Users of Apple's iCloud, which provides a single login for a number of services including Mail and Messages, are seeing authentication errors, with the problem coming just minutes before the company released the latest OS X 10.8.3 update.
Update: As of 3:02 Pacific, the iCloud login issue has been resolved.
The problem, which manifests itself as a password or user ID error, is limited to iCloud's Account and Sign In feature, which could affect user access to other services like Messages. Apple notes that all other iCloud assets operating normally, meaning that users who are able to authenticate their accounts with the attached services will go unaffected.
From the Status Webpage:
Users may incorrectly receive an authentication error when attempting to use iCloud. Setting up a new iCloud account from an eligible device may be temporarily unavailable.
It is unclear if the iCloud problems are related to the OS X release, and Apple has yet to offer additional information regarding the matter.