Computer systems used by the Obama and McCain campaigns were reportedly hacked over the summer by an unknown "foreign entity," according to an account of the attacks published Wednesday.

The sophisticated cyberattacks has prompted a federal investigation, Newsweek reported Wednesday. Attacks on both campaigns were similar in that investigators believed a foreign entity or organization sought to steal information on policy positions. Such information could be used in negotiations with the future administration.

Tech experts at the Obama headquarters initially believed that the computer systems had been invaded by a computer virus. The next day, however, they were told by the FBI and Secret Service that the problem was far more serious, the magazine reported.

"You have a problem way bigger than what you understand," an agent told Obama's team, according to Newsweek. "You have been compromised, and a serious amount of files have been loaded off your system."

Federal agents told Obama's aides that the McCain campaign had suffered a similar attack, which a top McCain official later confirmed to Newsweek.

[Editor's Note: This story has been redacted to remove a portion of the story unrelated to the hack.]