I logged in to Twitter and a few minutes ago and I was shocked to see this:

It seems like Twitter is infected with a bug or a virus. According to some, Twitter is infected with a mouseover security flaw that automatically sends DM or retweet other's tweets without the user's consent.

To know more, read this: http://mashable.com/2010/09/21/twitter-mouseover-bug/

The good news is.. we can still tweet by using Tweetdeck or any other Twitter clients because only the Twitter.com website was infected by the bug. :)