Everyone who uses social media will either knowingly or inadvertently allow access to third party apps. ReadWrite Social advises:
So don’t wait until your Twitter account is hacked. Take some time right now to clean things up and eliminate the apps that you no longer use or find relevant to your social networking way of life.
The article gives step by step instructions (via screenshots) on how to eliminate the third party apps that you either forgot about, no longer require or have no idea how they gained access to your account. Worth checking out.