It's indisputable at this point that AT&T blocked 4chan—what's 4chan, you ask?—the cesspool that has spawned some of the internet's greatest memes, like LOLCATs. We hear it's because of a massive DDoS attack emanating from that IP address.
Whatever the reason, the fact that AT&T won't officially comment on the matter virtually confirms that they were taking some action against 4chan earlier today. If there wasn't a valid security reason for blocking access to the site, then AT&T's actions are deeply troubling, to say the very, very least.
Access has since been restored, but expect the reprisal from 4chan—like planting the story that AT&T CEO Randall Stephenson died outside his house—to continue. 4chan's Moot says AT&T has yet to contact them. [4chan, TechCrunch]