While not a "scientific" hoax, I think an April Fool's Day salute is in order to my favorite forger of all times,
Hans Van Meegeren. Van Meegeren painstakingly forged a number of Vermeer paintings, selling the fakes to the Nazi hierarchy including Hermann Goring. Following the war, Dutch officials sought to prosecute him for selling national treasures to the nazis, forcing him to admit to his acts of forgery for which he was tried and convicted instead.
Any guy who swindles nazis is good in my book :-)
Van Meegeren's "Christ at Emmaus" originally attributed to Vermeer