From isc.incidents.org:
] Starting at around 8:30 am EDT (12:30 UTC), a number of
] sources started to report a widespread Akamai DNS issue.
] Large web sites, which use Akamai for its DNS service, no
] longer resolved in DNS, and became inaccessible to their
] users. The affected sites were Yahoo, Google, Microsoft,
] FedEx, Xerox, Apple and likely many others. The situation
] improved around 10:30 EDT, mainly because some of the
] affected domains temporarily switched from using Akamai
] DNS servers to their own DNS servers.
]
] The problems seem to be attributable to a DDoS attack on
] Akamai's DNS servers, though we do not presently have the
] information to make a definitive assessment. According to
] the Akamai spokesperson, the problem was not limited to
] Akamai. He attributed the outage to an attack on the
] Internet infrastructure on a larger scale. We do not
] currently know of any sites that were affected by the
] attack without using Akamai's services.

At least it wasn't the Roots/GTLDs..

According to Netcraft, it also effected antivirus update services for Symantec and TrendMicro.