Over the weekend, you may have received an email about getting $10 from Facebook(NASDAQ:FB). While such messages are usually spam or scams, this one is actually legit.

It’s part of a legal settlement over Facebook’s “Sponsored Stories” system, which based ads on the Likes of users — without their permission or payment. The company has set aside $20 million in a fund to pay the obligations.

But of course, there are some important extra details. For example, about $8 million will go to attorney’s fees. This is always the first priority.

Oh yeah, and the claimants may not necessarily get $10. The amount will depend on how many respond. If a ton do so — which seems likely — then there will be no distribution if the average claim is below $5. In this case, the $12 million will go to various privacy charities.

Now, if you still want to sign up, you can do so even if you deleted the email. There’s a Web form where you can make your claim. The deadline is May 2.