How Twitter can just about stop spam dead.

In an effort to stop spam Twitter needs to improve it's privacy options. Every day I get replies/mentions from people I don't follow and who don't follow me, all they are doing is spamming and I'm tired of blocking them.

The best solution is for updates to be protected as they are now, but with the option of still being visible to users and bots, add to that the option of reply only being available to approved people. Companies can then get see tweets about them with a right to reply, but users are able to control who can reply.

Mere protect or unprotect is about as colorful (or helpful) as mere black or white, yes or no, there is no middle ground, no customization - just lots of spam.

There would still be the problem of who to accept as a friend or not but this can be improved significantly with a user rating system; spammers would get a low rating by people and when a minimum number of votes is reached they get automatically blocked or add to the list of "friend requests" depending on the blocked/followed ratio.

Users should also be able to whitelist others should they actually want to follow a spammer, though this should not influence the above mentioned ratio as spammers will just approve themselves with multiple accounts.
Doing the above will significantly increase the value of Twitter Inc. and allow the many other improvements users have been wanting literally for years.