WordPress was forced to shut for nearly two hours after a core router change "broke the site".
Over 10 million blogs, including tech sites like TechCrunch and GigaOm, were affected, losing the all the WordPress bloggers an estimated 5.5 million pageviews.
The site acknowledged that the blogs were first down at 2PM Pacific time on the 18th on its twitter feed.
WordPress.com founder Matt Mullenweg said it was the firm's "worst downtime in four years".
On the company blog, he denied that security was an issue and that the downtime was not due to hacking or hit by a denial of service attack.
"I know this sucked for you guys as much as it did for us — the entire team was on pins and needles trying to get your blogs back as soon as possible,” he said.