Unclaimed prizes are kept by the lottery jurisdiction. If a Grand Prize goes unclaimed, the money must be returned to all lotteries in proportion to their sales for the draw run. The lotteries then distribute the money, based on their own jurisdiction's laws, to other lottery games or to their jurisdiction's general fund, or otherwise as required by law.
The only way to be sure that what you are buying is “official” is to purchase your tickets from a company that has agents that will purchase in the real world the Powerball tickets online that you have selected. If you are a more trustworthy person and don’t need a scanned copy of your Powerball tickets online then by all means go for an online lottery ticket provider that follows the insurance model. 
Even though some scratch cards costing as much as $50 in Texas and $30 in Massachusetts, state lotteries are exempt from Federal Trade Commission “truth in advertising laws” The Federal Communications Commission prohibits the broadcast of lottery advertisements, but has exemptions for lotteries “conducted by a state acting under the authority of state law. Hence, TV commercials like “The Possibilities are Endless.” (Lotteries raise over $70 billion a year, according to the North American Association of State and Provincial Lotteries. Profits from the Powerball are used to fund public projects approved by state legislatures.)
On June 2, 2010, Ohio won a Powerball jackpot; it became the first lottery selling either Mega Millions or Powerball (when 2010 began) to provide a jackpot-winning ticket for its newer game. The ticket was worth a $261 million annuity; it was sold in Sunbury. Ohio's second Powerball jackpot-winning ticket, sold for the June 23, 2010 drawing, was part of another first; since Montana also provided a jackpot winner for that drawing, it was the first time a jackpot was shared through lotteries which sold competing games before the cross-selling expansion, as Montana sold only Powerball before the expansion date.
The US Powerball is a standard lottery draw game based and operated from the golden State of California. The US Powerball has been making millionaires and multi-millionaires since its first drawing way back in 1992. With over 25 years of experience in the lottery industry, the Powerball, along with many other State lotteries, has broken through the final glass ceiling and transformed itself from an interstate lottery into a truly international lottery of global reach. 
×