Twitter was recently affected by the twitter worms because of which there was a great rucus. It’s live right now too. So here’s a quick solution -

If you are not infected

Please stop using twitter’s web interface and use Apps like TweetDeck for twitter

If you are infected

Reset your Password , clear your Browser Cache or try rerreshing your twitter settings to get back to normal. Mostly u might lose your Twitter Bg, but you can set it back by going to twitter settings >> Design.