Source: Ricky Rodriguez via Twitter
Reports of the intermittent outages first began at around 6:30 p.m. Eastern when users took to online message boards and Twitter, voicing concern over error messages seen on the iTunes Music Store. As of this writing, the issue seems to have been rectified.
The scope of the issue is unclear at this time, though further investigation found bad DNS entries on Google DNS and Speakeasy to blame for the partial outage. Extrapolating from information available, it appears bad DNS entries first showed up on the two major DNS providers, which then propagated elsewhere around the globe.
While no official statement has been issued, some users speculate that the erroneous DNS entries are the result of a hack. At this time, there is no evidence to support the theory, but it could be a possibility.
Services affected by today's DNS issue included iTunes, the App Store and parts of Apple's webpage, while others like iMessage and Game Center were left untouched.