On the internet, you have more or less equal footing with any opponent. If you're being physically bullied, you're probably at a physical disadvantage, but online, your ability to protect/defend yourself or retaliate is entirely on par with an adversary, and if you cannot or will not, no law can protect you, on the internet or otherwise.
That said, I think that mob violence against bullies of any sort could potentially be justifiable, so what do I know?