Anonymous
You're only anonymous if NOBODY knows who you are. The principle of the internet group of that name ought to be that nobody knows anyone else's real identity, so that if any member is "doxed" (=documented, real identity revealed) he can't dox anyone else.
This, however, creates impossible logistic problems. How can you organise anything secretly if you have no way of knowing who you're talking to? How can you spot an infiltrator? Sure, you can use impenetrable encryption, but how can you be sure you're sending the keys to someone you can trust? Complete anonymity renders you impotent, and every person you reveal your identity to introduces an exponential security risk.
The world's police forces (around a decade behind in technology, as usual) are now realising that they can win against such "anonymous" groups because of the above logic.
Whilst Anonymous, LulzSec, et al may have given us a few laughs this year, I suspect that the kind of thing they've been doing will remain a fringe activity, and will cease to be news in a few years.