Daniel Spitler, 26, admitted that he was a member of Goatse Security, a loosely organized hacking group named for an obscene Internet meme that says its mission is to expose security flaws.
Spitler and another man, Andrew Auernheimer, were charged in January.
U.S. Attorney Paul Fishman said in a statement, “Computer hackers are exacting an increasing toll on our society, damaging individuals and organizations to gain notoriety for themselves. In the wake of other recent hacking attacks by loose-knit organizations like Anonymous and LulzSec, Daniel Spitler’s guilty plea is a timely reminder of the consequences of treating criminal activity as a competitive sport.”
AT&T’s security measures were heavily criticized in the wake of the hack, which exposed 114,000 e-mail addresses.