Twitter first crashed around 12:30 p.m. EDT on Thursday. The outage affected all platforms and took down both third-party and Twitter apps on the Android and iOS platforms.
The site returned around 1:15 p.m. In a blog post Thursday night, Vice President of Engineering Mazen Rawashdeh, said Twitter engineers found a cascading bug in one of Twitter's infrastructure components. That means the bug didn't just hit one particular software element, but "cascaded" across the system, he said. "This wasn't due to a hack or our new office or Euro 2012 or GIF avatars, as some have speculated today," Rawashdeh added.
"One of the characteristics of such a bug is that it can have a significant impact on all users, worldwide, which was the case today. As soon as we discovered it, we took corrective actions, which included rolling back to a previous stable version of Twitter," he added.
Twitter denied claims from a hacker group that it was responsible for Thursday's outages.
Shortly after the outage was fixed, Computerworld and other news organizations received an email from someone claiming to be a member of UGNazi, also known as the Underground Nazi Hacktivist Group, claiming that it was responsible for the Twitter outage.
The email claimed it took down Twitter with a distributed denial of service (DDoS) attack.
"Twitter supports the CISPA bill and we wanted to show what we really are capable of," the group said in a separate email.
The CISPA, or the Cyber Intelligence Sharing and Protection Act, is a controversial cybersecurity bill that, if enacted, would increase the information that is shared between technology companies and the government.
Gartner security analyst Lawrence Pingree said UGNazi could have launched an attack on Twitter today but that may have only been coincidental.
"If a company is being taken down by a third party, I don't really see them blaming themselves," he said. "Are [hacking groups] capable? Yeah. Denial of service isn't something you can completely stop [but] it's hard to say if there was an attack."
Chet Wisniewski, senior security advisor at Sophos, is skeptical of UGNazi's claim.
"There is no reason to believe the outage was due to any activities by UGNazi or others who say they were responsible for the outage," said Wisniewski.
"Ultimately, the only organization that knows the truth is Twitter, and there is no reason to believe the statements they have made are not true. It is difficult to determine the exact nature of the outage from the outside, but my personal experiences during the outage are more consistent with Twitter's explanation."
Sharon Gaudin covers the Internet and Web 2.0, emerging technologies, and desktop and laptop chips for Computerworld. Follow Sharon on Twitter at @sgaudin, or subscribe to Sharon's RSS feed . Her e-mail address is email@example.com.
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This story, "Twitter Downplays Downtime" was originally published by Computerworld.