The FBI believes foreign hackers targeted the computer of retired Admiral Mike Mullen, the former chairman of the Joint Chiefs of Staff, in what is thought to be the latest in a pattern of attacks on computers of former high-ranking U.S. officials.

The report first surfaced in The Wall Street Journal after Mullen's office confirmed to the news site that the retired admiral was cooperating with a cyber investigation.

"Adm. Mullen, now a private citizen, has responded to very specific requests and is cooperating with an ongoing cyber investigation he has been informed is focused overseas," said Mullen's office.

The Wall Street Journal says officials and others familiar with the probe confirmed that hackers targeted personal computers Mullen used while working on the grounds of the U.S. Naval Academy in Annapolis, Maryland, after his retirement in 2011.

Fingers are already being pointed at China, a country which has in the past been accused of government-sponsored cyber attacks.

In June 2011, Google accused hackers in China of orchestrating an attack on Gmail accounts of hundreds of users including, among others, senior U.S. government officials, Chinese political activists, officials in several Asian countries, military personnel, and journalists.

"The goal of this effort seems to have been to monitor the contents of these users' emails, with the perpetrators apparently using stolen passwords to change peoples' forwarding and delegation settings," said Google in a blog post at the time.

That wasn't the first time Google has suggested high-level hacking activity originating from China, either. In 2010, the search giant was forced out of doing business in the country following hacking activity linked to senior Chinese figures.

Geng Shuang, a spokesman for the Chinese Embassy in Washington, told The Wall Street Journal that he wasn't aware of the investigation into the hacking of Mullen's computers, and that his government prohibits cyberattacks.

"China is a major victim of hacker attacks," he told the news site. "The Chinese government would like to work with other countries, including the U.S, to explore effective ways to combat cyberattacks."

Mullen was one of five people named to a State Department board last month to review the events surrounding the attack on the U.S. consulate in Benghazi, Libya in September. Mullen also serves on advisory boards at the State Department and Central Intelligence Agency and has access to classified information.