It has long been known that Arafat stole and hidden away vast sums of money. Most of the money came from embezzling a percentage of donations that were supposed to go to the Palestinian people. At this point, his personal wealth is estimated to be between $2 and $3 billion, and no one knows where it's stashed away. According to this article
, part of the reason he is being kept on life support is in the hope that he will awake and disclose where the money is.