Centsports.com has become very popular over the past two years. For those unfamiliar with Centsports, you watch an ad and you get .10 cents to gamble on sports games. 
The website claims that the website is legal, because no money is ever deposited into the website. This is the most recent interview with the founder.
The website claims that the website is legal, because no money is ever deposited into the website. This is the most recent interview with the founder. I have doubts about the supposed legality of the website. Sports betting is sports betting. They can argue that nobody ever put up any money and it's all "for fun". The DOJ will argue it's sports betting as covered under the Wire Act and players and the site are making money. Money is being made by watching the ads, and that cash is being used to gamble on sports online. The Wire Act states:
Whoever being engaged in the business of betting or wagering knowingly uses a wire communication facility for the transmission in interstate or foreign commerce of bets or wagers or information assisting in the placing of bets or wagers on any sporting event or contest, or for the transmission of a wire communication which entitles the recipient to receive money or credit as a result of bets or wagers, or for information assisting in the placing of bets or wagers, shall be fined under this title or imprisoned not more than two years, or both.
It's money, people are wagering on sports, and the site is presumably profiting from it. This sounds awfully like the business of wagering on sports, as covered under the Wire Act.
The DOJ probably won't come after the bettors, but they'll go after the site's owner. It doesn't help that the kid who runs the site lives in the United States, Texas to say the least. If he gets "investigated", I'll be willing to bet top dollar the site will buckle. On that corollary, whenever you can reasonably cash out, you should do so. There are no guarantees with this site.
What centsports is hoping is that if they stay a small fish (betting cents), they'll be under the DOJ radar. Considering the DOJ priority shifts, current resistance from online gamblers, and the new presidential administration, it's not a completely stupid decision. It's still a stupid decision though, because the site owner is gambling with jail time. To put it bluntly, jail sucks, so the EV of the crime better be worth the probability of jail time.
The reason why the site refuses to post anything regarding its legality is because it's probably not legal. No reasonable lawyer will advise otherwise. Simple enough explanation.
I would put the odds of any prosecutor argument being successful in this particular case at 85%. That's just my educated guess.
www.betmystock.com is another good one with the same concept and only $15 cashout