First of all, if your brother's site has any real value then you should seek proper legal advice from a lawyer, don't rely on the half assed reposnses we're likely to give you. If, on the other hand, this is more a case of you brother being rightfully miffed at someone stealing his work but that work having no real value then I'd suggest a cricket mat to be a particularly effective measure.

What your brother can do about about it legally depends very much on the country he's in and the country the guy who nicked his source code is in but generally you don't need a copyright to defend intellectual material (although thye're very useful). You merely need to be able to prove that you created it and you did so before anyone else did. Essentially, all the copyright you put into your software really is is a timestamp and a warning to anyone else not to pinch it so they can't deny later that they knew you considered it your own intellectual property.

It's common practice in the music business (and I believe this happens in publishing as well) for people to post their work to themselves and then leave the envelope unopened. That's because the post office will time stamp the envelope so you can trivially prove later that you had created the work before that date. I'm not sure if you're aiming to prevent someone pinching your stuff or seek redress from someone who already has but if it's the former then this is quite a neat and convenient trick.

If your seeking redress then get some proper legal advice. Depending on the value of your brothers work you might want to go to a formal claims court or you might just want to pursue it through small claims court. Actually, just a threat that you're going to pursue it is likely to be enought to get them to take their site back down.