Using a DoS attack on someone elses server should fall under cyber crime/war/terrorism protection. If fox has that done to a server based in the US i hope a cyber defense unit will shoves a nuke up their asses to stop them from committing felonies to stop misdemeanors.
I am fairly sure vigilante justice is still illegal. If your neighbor steals your lawn mower, you are NOT allowed to go over to his house and shoot him (though, in some states, you might get away with it if you caught him on your property stealing it).
Still, is this an Indian firm attacking sites based in India, cause I have no idea what the laws are like there. If this is an Indian firm attacking sites based in other countries, that borders on international crime. Still, I don't think too many torrent sites are hosted in the U.S. so I really don't know what law would apply here. I would like to think that no one would be allowed to do this in the U.S. (hopefully).
So, let me get this straight... A criminal act of cyber-terrorism is OK because an agent of a rights-holder claims (but has not proven the claim to any legitimate judicial body in any country or jurisdiction) that you are infringing... I hope these guys annoy the 4chan folks, because a reverse DDNS attack that cripples a large chunk of the Indian local internet (which is, in theory, the largest democracy in the world) would be unfortunate... But, very, very funny.
First of all, I assume you mean a DDoS attack. A simple DoS attack would be ineffective and almost immediately dealt with by the server's firewall.
Second, a DDoS originating from a particular geographic region is almost as easy to block and would simply result in huge blocks of IP addresses belonging to Indian service providers being blocked.
The only way to launch an effective DDoS is to use a botnet with a large geographic distribution. However, this is highly illegal on many levels. Not only are you engaging in an attack which violates federal, state and local laws, you are also illegally comandeering and using computing resources belonging to countless private citizens, business, and even government entities (each of which is a separate charge of illegally accessing a computer).
Suffice it to say, this is the most illconceived idea I've heard of in a LONG time.
The BIGGEST problem in cyber security is not, as you might think, how to deal with cyber threats, but something called: attribution. In simple terms... who is responsible. If you own up to doing something like this, it would be like posting on Facebook that you intend to rob a bank because they short-changed you.