I'm posting this here because I know a lot of us use Twitter. Twitter is currently under attack from hackers who are exploiting a bug in Twitter's code. If you use twitter.com, you can inadvertently retweet spam and porn to your followers, just by hovering over other tweets.
Third party applications are safe. Only use those until the problem is resolved. I recommend HootSuite or TweetDeck.
There's a New Twitter Exploit and It's Spreading Like Wildfire