The hacker has already posted tons of stolen material online he ransacked from the AOL account of 53-year-old Dorothy Bush Koch -- including private pictures of 88-year-old President George H.W. Bush while he was being treated in the hospital.
There's also a photo of George H.W. Bush with Bill Clinton ... and one shot that appears to show Dubya painting on a canvas.
the hacker watermarked the pics with his online alias -- "Guccifer."
Guccifer claims he/she was able to expose 3 years of information -- material dating from 2009 to 2012.
Guccifer also released home addresses, cell phone numbers and emails for a bunch of Bush family members.
The secret service is investigating the matter.