A message has been published under her name which appears to promote "fat-burning" methods and contains a link to Tumblr.
The account is currently set to private but users who already followed her were able to see the message.
"It's obviously been hacked and is pretty crude," a family spokeswoman said.
Twitter have yet to respond with a statement.
Peaches died in April. Initially the cause was unknown, but it was later linked to heroin use.
Her body was found by her husband Tom Cohen at their home in Wrotham, Kent.
She had two sons, Astala, two, and Phaedra, one.
In an interview last month, Sir Bob Geldof said he "blames himself" for the death of his daughter.
He described the journalist, model and TV presenter as "super bright" but "frantic" in her private life.
"You blame yourself," he said. "You're the father who is responsible and clearly failed.
"For anybody watching, who has a dead kid and you're a parent, you go back, you go back, you go over, you go over.
"What could you have done? You do as much as you can."
Follow @BBCNewsbeat on Twitter and Radio1Newsbeat on YouTube
The Twitter account of Peaches Geldof, who died earlier this year at the age of 25, appears to have been hacked.