The WordPress blog hosting service came back online this afternoon after several hours of pummeling by a relentless distributed denial-of-service (DDoS) attack that either slowed or knocked offline its 18 million blogs.

This was the largest DDoS attack ever against WordPress, reaching the capacity of multigigabits per second and tens of millions of packets per second, according to WordPress' Twitter update. The attack took its toll on all three of the site's data centers, which are based in Chicago, San Antonio, and Dallas, and

WordPress told Sophos, which uses the platform for its Naked Security blog, that it's getting outside help in thwarting the attack. "The DDoS is too large for us to mitigate directly, so we've been collaborating with our upstream providers and relying on their intervention. This is a precision interventional, so potentially the attack could be shifted around it," according to WordPress.

"This is the largest and most sustained attack we've seen in our six-year history. We suspect it may have been politically motivated against one of our non-English blogs, but we're still investigating and have no definitive evidence yet," WordPress founder Matt Mullenweg told CNET.

Nicholas Percoco, vice president at Trustwave and head of the company's SpiderLabs ethical hacking team, says that if it were a politically motivated attack, then it could have been via a rented botnet. "And if they were pointing toward a [specific] blog on WordPress, it would take down all of the blogs" on the site, Percoco says. "It's cloud-based, so everyone shares the same resources. If WordPress is watching the [DDoS] trafic, they can see immediately who it's going toward."

While WordPress is mainly known for its consumer blogging service, it also offers a premium VIP service for corporate customers, such as Sophos, that host their blogs via the service.

WordPress was not available for comment at the time of this posting.

Just how the company is handling the mitigation of the attack remains unclear, but Trustwave's Percoco says there are several ways to fight a DDoS. "There are tricks you can do," he says. "If you know the specific targeted blog, you can reroute that traffic someplace else to a dark space that's not impacting the environment," for instance, or shift IPs.

"There are things you can do -- but they aren't permanent solutions," Percoco says. There's only so long that you can "dance around and dodge bullets" in this fashion, he notes.

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