There is a "devastating scale" of neglect and abuse experienced by adults with autism, a charity has warned.
Many are staying at home because they are afraid of being abused or harassed, the National Autistic Society (NAS) said.
People with autism can find it hard to interpret other people's motivations and as a result can be taken advantage of or manipulated, the charity said.
Half of 1,300 sufferers questioned by NAS said they had been abused by someone who they thought of as a friend, 37% said they had been manipulated to do something they didn't want to do by these so-called friends and 44% said fear of abuse or harassment led them to not wanting to leave the house.
Meanwhile a quarter of those polled said they have had their money or possessions stolen.
The charity said that the poll also revealed that many adults with the condition are being neglected.
Two thirds said they require someone to prompt them to wash, dress or feed themselves. But seven in 10 of these sufferers said they had missed meals because they don't get this support and 86% said they had not washed.
NAS raised concerns that changes to the care system could mean this kind of neglect could become more commonplace. A spokesman said that the Government's proposals suggest that people will be eligible for care and support if they need "assistance", which may not necessarily include prompting.
Mark Lever, chief executive of NAS, said: "These alarming figures paint a depressing picture of the horrendous abuse and neglect experienced by many adults with autism.
"We have heard deeply distressing stories of men and women living in utterly intolerable conditions, exploited physically and financially by supposed friends or unable to care for themselves without support.
"One professional told us of a man who had been found at home suffering from severe malnutrition and with mould growing on his skin as he was unable to feed or clean himself without prompting. This is utterly unacceptable in 21st century Britain.
"We know that many people with autism are able to live relatively independent lives, but many others need support to stay safe and healthy.
"The Government's changes to the care system offer a chance to support these at-risk individuals. However, we are incredibly concerned that the current proposals as they stand do not recognise the basic needs of these more vulnerable people with autism.
"It's not too late. The eligibility criteria must be revised so that they explicitly recognise the support needs of those at risk of abuse and neglect and protect some of the most vulnerable people in society."