[Update: Apple's services are back online as of this writing (4:50 PM EST). - Bryan]
Apple experienced a rare online services outage Wednesday, an outage that made iCloud, Mac App Store, App Store, iBooks, and iTunes Store inaccessible. The company said in a statement it was due to an internal DNS error, and apologized for the outage.
"We apologize to our customers experiencing problems with iTunes and other services this morning," Apple said in a statement to CNBC. "The cause was an internal DNS error at Apple. We're working to make all of the services available to customers as soon as possible, and we thank everyone for their patience."
Apple maintains a System Status page for all of its online services—it's a good place to check when you're experiencing a problem with those services. As of this writing, App Store, Mac App Store, iBooks, and iTunes Store all remain "Unavailable for all users."
This is what you'll see if you pull up the Mac App Store:
Mac App Store "Cannot Connect to the App Store."