The FBI contacted Earthlink and AOL on Tuesday to aid in the investigation of the terrorist attacks on America.
Dan Greenfield, vice president of communications at Earthlink, said his company was contacted to assist the FBI, but could not disclose the details of the investigation.
"We are fully cooperating with the FBI investigation of Tuesday's events, as we would with any investigation, " Greenfield said.
According to a CNN report, the FBI also served search warrants to AOL and Yahoo. An Earthlink executive said the FBI is serving warrants to all the ISPs, CNN reported.