If you see a tweet like the following it is a phishing scam
FYI this profile on twitter bit.ly/VUbiVa is spreading nasty blogs around about you
How does the scam work?
Usually you receive this tweet as a direct message (which can only be from somebody that follows you). It is likely that you will know them so you are more likely to trust the message.
If you click on the link it will take you to a page that looks like a twitter login. If you login you are giving away your twitter username and password to a scammer. The scammer can now log in to your twitter account and send hundreds of direct messages to your twitter followers. So the cycle continues and your followers trust the message because it has come from you.
What can I do about it?
Do Not click on the link. What you can do is to contact the person who sent you the message and advise them that their twitter account has been compromised. (You could tweet them a link to this article)
What they need to do is immediately change the password to their twitter account. If the cannot login they will need to contact Twitter Support to let them know that their account has been hacked.
Is my Twitter account safe?
As long as you have not used the fake twitter login you should be OK. To make sure it is worth checking what messages you are sending from your Twitter account now and then. If you see you have been sending messages similar to the above (i.e. you didn't send them) you have been hacked and you need to change your password ASAP.