Have you ever logged in to Twitter to see that you have been posting, mentioning people or maybe even sending instant messages to people but you haven’t been near your account for hours? It happens. When it does, provided you haven’t given some rogue programmer or site master your login information, you can control access to your account. There are several legitimate applications who ask for permission to access your account for varying reasons. Seesmic, for example, needs to be able to login as you, post as you and send instant messages as you. Paper.li needs to be able to read as you to work and wants to post as you so it can spam all of the people it copied when it posted.
You can turn off access to your Twitter account to any application using the Twitter API by following some very, VERY simple steps. Watch this short video on YouTube for a quick walk-through showing exactly how to do this.