A computer hacker has broken into email accounts belonging to former US presidents George H.W. Bush and George W. Bush, as well as other members of their family, US media report.

The hacker apparently intercepted photos that George W. Bush emailed to his sister showing paintings that he was working on, including self-portraits of him showering and in a bathtub, one report said on Friday.

Another leaked picture showed the elder Bush in a hospital bed, a snapshot purportedly taken by his daughter, whose AOL account was among those that was apparently hacked.

"There's a criminal investigation under way," Jim McGrath, a spokesman for the elder ex-president Bush, who is now aged 88 and was recently hospitalised, told AFP news agency, following reports that private communications had been accessed.

"I can't get into the specifics," McGrath added.

The investigative website The Smoking Gun reported that hackers had accessed several e-mail accounts and then published personal photos and private correspondence belonging to the former US leaders and their loved ones.

Separate email accounts used by prominent figures including CBS sportscaster Jim Nantz, a longtime Bush family friend, and others were also breached.

'Veteran hacker'

According to The Smoking Gun, six separate e-mail accounts were compromised. The authenticity of the photos and other details on the website could not immediately be confirmed.

Secret Service spokesman George Ogilvie said the agency was investigating. He would not elaborate.

The word "Guccifer" was plastered across the photos published on the website, which quotes "Guccifer" as describing himself as a veteran hacker who has long been in the government's sights.

Free email accounts from commercial providers are especially vulnerable to hackers who exploit easy-to-use features to reset email passwords.

AOL's email passwords can be reset by a hacker who could discover, for example, the birth year of a customer's mother, a father's middle name or the name of a favorite pet.

Last year, after The Associated Press revealed that Republican presidential candidate Mitt Romney and some top aides had used private email accounts to conduct state business at times when Romney was governor of Massachusetts, Romney's free Microsoft Hotmail account was hacked.

The alleged hacker claimed to have guessed the answer to a security question about Romney's favorite pet in order to gain access to the account and change the password.

The anonymous hacker said Romney's account on DropBox, a file-sharing service, also was compromised.

A college student in Tennessee, David Kernell, was convicted in April 2010 on federal charges of hacking into Sarah Palin's private emails weeks before the 2008 presidential election.

Kernell had correctly guessed answers to security questions guarding Palin's account, giving him access.