The US Secret Service is investigating how the hacker gained access to material such as pictures of the older Mr Bush in a hospital bed and the four-digit security code for a gate to one of his son’s homes.

He also obtained a confidential list of home addresses, mobile phone numbers and email addresses for dozens of members of the Bush family, including the former presidents, their siblings and children.

Self-portraits painted by the younger former president – two of which depict him relaxing in the bath and taking a shower – were also published on the internet by the hacker, who called himself Guccifer.

The material is believed to have been gleaned from messages that were sent between 2009 and last year and stored in six different email accounts belonging to Bush family members and their friends.

“Why would someone do this?” Dorothy Bush, the youngest child of the older Mr Bush and his wife, Barbara, asked The Smoking Gun, a website where some of the hacked material first emerged.

Detailed information about the younger Mr Bush’s plans for playing golf with friends were also obtained in the hack. He remains protected around the clock by government agents.

Spokesmen for the former presidents declined to comment. Jim McGrath, an aide to the older Mr Bush, would only tell the Houston Chronicle that the matter was “under criminal investigation”.

A hacked message sent last December by Jean Becker, his former chief of staff, shed light on the ailing health of the older Mr Bush, who was at the time being treated in hospital after being taken ill.

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