The company posted notice of the attack on its dashboard Web page that the attack started at 4:05 GMT today with a brief explanation of the problem.
"Unfortunately, the DDoS attack from yesterday returned in a different form this morning and affected site-wide performance," the site says. "The good news is that we were able to mitigate it quickly and performance returned to normal around 11:15 [GMT]. We are continuing to monitor the situation closely."
The company still doesn't know why it was attacked, but speculation is it was an attempt to muzzle political blogs it hosts.
"There's a rumor floating around that the attack may have been politically motivated, but right now I haven't seen the proof to back up that claim," says Roel Schouwenberg, a researcher at Kaspersky Labs. "Currently, we don't have any detailed information as to who may be behind the DDoS."
Wordpress.com referred to yesterday's attack as the largest in its history, and efforts it made then might have reduced the impact felt from today's attack. The company said it was seeking help from service providers that connect it to the Internet to filter the attacks before they hit Wordpress.com servers.
The company's founder Matt Mullenweg had no proof but said he suspected the attackers were provoked by "one of our non-English blogs."
Distributed DoS attacks are gaining in popularity, according to Kaspersky. They are both more frequent and more severe. "I know of quite a few businesses that had the DDoS-problem under control until the attacks started to intensify recently," Schouwenberg says. "Possibly the high-profile DDoS attacks of late have functioned as some form of inspiration for other people."
The scale of yesterday's attack was beyond anything the company had seen before, with rates of multiple Gbps, representing tens of millions of packets per second," throwing off the company's three data centers in Chicago, San Antonio and Dallas.
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