What exactly does it do?
The bill creates a blacklists of Internet domain names which the Attorney General can add to with a court order. Internet service providers, financial transaction providers, and online ad vendors (everyone from Comcast to PayPal to Google AdSense) would be required
to block any domains on the list.
(The bill used to also have a second list that the AG could add to without a court order, but public pressure has gotten it removed.)
What kind of domains can go on the list?
The list is for domains "dedicated to infringing activity," which is defined very broadly — any site where counterfeit goods or copyrighted material are "central to the activity of the Internet site" would be blocked.
What's so bad about that?
Well, it means sites like YouTube could get censored in the US. Copyright holders like Viacom argue that copyrighted material is central to activity of YouTube. But under current US law, YouTube is perfectly legal as long as they take down copyrighted material when they're informed about it -- which is why Viacom lost their case in court. If this bill passes, Viacom doesn't even need to prove YouTube is doing anything illegal -- as long as they can persuade a court that enough other
people are using it for copyright infringement, that's enough to get the whole site censored.