Removing and preventing fake accounts should be they're no. 1 priority.
As for the fake accounts I think they flourish on Twitter not just because it is social media, but also because of the follower limits. There is a whole underground business of fake accounts to get real users over the 2000 follower mark initially and even higher as the account grows as followers to following becomes out of whatever proportion Twitter sets. I think if they eliminated or adjusted the 2000 follower limit (there are other ways to detect spam accounts besides limiting the account to 2000 followers until they cross a threshold) it would help some with deterring this issue.
Sorry rant over :)
These fake accounts are quite difficult to detect.
The accounts that are easy to detect are avoided anyway, since users get to manage their own subscriptions. Some are even cherished for their novelty - horseebooks, etc.
Detecting these covert accounts means being a middle man for whichever party lays a claim about source - and this makes Twitter a middleman for other parties' curation.
They will submit requests to have these taken down (as the State Department did to Youtube to take down Al-Alwaki's videos) - though currently Twitter is not very cooperative.
I do not know how Twitter would handle a problem like this itself.
I fear they might be tempted to attack the later by attacking the former.