Andrew Auernheimer is being held in jail in Fayeteville, Arkansas, according to police officials.
He was arrested earlier after FBI agents said they discovered illegal drugs in his dwelling. The agents were executing a search warrant that was obtained in connection with their investigation of the AT&T breach.
Auernheimer belongs to Goatse Security, a group that comprises a handful of self-styled computer security "researchers." Goatse members have admitted to breaking into AT&T's servers and obtaining the e-mail addresses of more than 100,000 iPad users. The group said their intention was to expose AT&T security vulnerabilities.
Among the e-mail addresses obtained by the group were those belonging to high-profile individuals like New York City mayor Michael Bloomberg, White House chief of staff Rahm Emanuel, and Hollywood producer Harvey Weinstein.
In his profile on the business networking site Linked In, Auernheimer describes himself as an "8-year IT pro." Beyond his current affiliation with Goatse, he lists stints at software developer Aptworks and escrow agency First American Title Holding Company.
AT&T has said it plans to work with legal authorizes to prosecute the hackers who broke into its servers.
AT&T "does not tolerate unauthorized access to its customers' information or company websites," said AT&T chief privacy officer Dorothy Attwood, in an e-mail last weekend to iPad users affected by the breach.
"We will cooperate with law enforcement in any investigation of unauthorized system access and to prosecute violators to the fullest extent of the law," Attwood said.
Attwood called Goatse's actions malicious. "The hackers deliberately went to great efforts" to obtain iPad owners' e-mail addresses, she said. The carrier said it has since fixed the vulnerability that gave the hackers access to its servers.