"The FBI is investigating this matter jointly with the US Secret Service,” a spokeswoman for the Federal Bureau of Investigation in Washington told Reuters. “As this is an ongoing investigation, we declined further comment."
The investigations began early this week when the hacker, who calls himself "Cracka" and claims to be working with a group of six people called CWA, or Crackas With Attitude, used a Twitter account to publish names, social security numbers, and phone numbers found in Brennan's email. The 20 individuals listed all worked for the Obama transition team in 2008.
On Wednesday, Wikileaks published more of the emails contained within Brennan’s AOL account, which included phone numbers, addresses, his wife’s social security number, documents regarding the CIA torture program, and more.
"The hacking of the Brennan family account is a crime and the Brennan family is the victim. The private electronic holdings of the Brennan family were plundered with malicious intent and are now being distributed across the web," the CIA said in a statement on Wednesday.
"This attack is something that could happen to anyone and should be condemned, not promoted. There is no indication that any (of) the documents released thus far are classified," the statement continued.
The hacker claims to have used social engineering to trick workers at Verizon into providing Brennan's personal information, and to have used that to subsequently dupe AOL and Comcast into allowing access to the target accounts.
WikiLeaks has stated they will be releasing more content from Brennan's account in the coming days.