A group of hackers known as UGNazi—yep, the same ones behind the multiple attacks on D.C. government websites and posting Mayor Vince Gray’s Social Security number online in April—have claimed responsibility for the Twitter outage that silenced the world’s tweeters for some 40 minutes earlier this afternoon, reports CBSAtlanta. Twitter disputes that account, saying it was merely a bug that crashed the social media service.

The main hacker behind the attack, Cosmo—who says her name is Hannah Sweet—just confirmed the group’s claim that it was behind the denial of service attack, in which servers are flooded with massive amounts of traffic at one time. “Yes, I did bring down twitter,” she said in an email.

Twitter, though, denies that hackers were involved, saying only that “Today’s outage is due to a cascaded bug in one of our infrastructure components.” Others are similarly expressing skepticism, noting that Twitter handles heavy traffic on a daily basis, so it would likely be prepared for something like this. (Twitter has been hacked in the past.)

During the April attacks, various D.C. government websites and servers were taken offline as part of an ill-targeted protest against the federal government. “We our attacking dc.gov because the way the government treats the internet,” Cosmo wrote us at the time. “It seems is if they don’t care about our input and for that they will pay. We were sending various attacks via Botnet to make the servers crash. We will be launching future attacks on DC.gov and various DC and government websites.” Around the same time the group attacked the NASDAQ website and NYC.gov, among others.

Cosmo was arrested by the FBI in late May, but according to her, “I haven’t been charged as of now.”