I would be worried about who put it there and why?! My next thought would be about calling my attorney. Of course, it would be much more fun to buy a few plane tickets and fly the family to a tropical island to hunt for a vacation home...
That would be nice, that is very smart. Instead of saying you would spend spend spend, you asked the correct questions. Where did it come from? Who put it there? Calling your attorney. Then spending it on family on trips and a vacation home, seems to me like money well spent with some money left over.
I would invest 50% in google shares and take the other 50% to viva Las Vegas, and carry on life as normal..
Hire hookers and snort coke with it all and be dead before sunrise when the cops start investigating and requesting the money to be returned.