"The FBI is aware of these possible computer intrusions and has opened an investigation to address the potential cyber threat," said Special Agent Jason Pack, an FBI spokesman.
The investigation is being overseen by agents from the FBI's Washington field office, according to FBI officials.
AT&T confirmed the data breach on Wednesday, saying user e-mail accounts may have been compromised.
"AT&T was informed by a business customer on Monday of the potential exposure of their iPad," AT&T spokeswoman Susan Bell said. "The only information that can be derived from the ICC IDS [customer identification system] is the e-mail address attached to that device. This issue was escalated to the highest levels of the company and was corrected by Tuesday; and we have essentially turned off the feature that provided the e-mail addresses."
It was unclear why the investigation was being run out of the FBI's Washington field office.
Shawn Henry, the assistant director in charge of the Washington field office, previously oversaw the cyber divsion at FBI headquarters.
Some high-profile government officials are known to use the iPad and it is possible government e-mail addresses may have been compromised.
FBI officials said the ultimate venue conducting the bureau's investigation could change depending upon where potential victims live and other factors.
Calling it the "most exclusive e-mail list on the planet," Gawker said the list of exposed owners included New York Mayor Michael Bloomberg, White House Chief of Staff Rahm Emanuel and other powerful figures in finance, media and politics.
The security hole was uncovered by Goatse Security, a group known among security experts as hackers who enjoy pulling Web pranks, Gawker reported. Still, the group previously has uncovered flaws in browsers Firefox and Safari, Gawker said.
When contacted by ABCNews.com, a man who asked to be named as a Goatse employee confirmed Gawker's report.
ABC News' Ki Mae Heussner contributed to this report.