How can I make my tweets private?

I want my tweets on Twitter to remain private and not be visible to anyone except those I designate as being able to view.

How do I accomplish this?

From web app jlech

• You need to check "Protect my tweets" on http://twitter.com/settings/account

  Only let people whom I approve follow my tweets. If this is checked, your future tweets will not be available publicly. Tweets posted previously may still be publicly visible in some places.

  From Al Everett

• I already mentioned this on a facebook thread, but it is worth mentioning again:

  If you are truly concerned about the privacy of twitter (or any social media) it would be prudent to communicate those messages in another format.

  From Jeff Epstein

• If your intent is to share your tweets only with coworkers, you may want to look at yammer.com.

  From Miro A.