How is that possible to hack someone's twitter?

Most of the time when you hear on the news or whatever that somebody's twitter got "hacked" what they really mean is "the twitter user is a moron who somehow got tricked into giving up their password."

To my knowledge, twitter has only been truly hacked once.

If a hacker has your nick he just needs to get your password and believe me, it's not that hard as you might think. It is all a matter how you expose yourself on the internet. You should protect the visibility of your social network accounts and do not leave any unnecessary information.

Yes its possible

the best thing is to come up with a really good password.

Nothing is impossible.

Try this, it works perfectly.