Today I was casually going through my Twitter settings and found that I had authorized many third party clients to tweet on my behalf. I had stopped using most of those clients, but I didn't know that these permissions are persistent (i.e. authorizations persist even after we uninstall the clients).
Leaving only the clients that I use currently, I revoked access to all other clients. You also go ahead to Twitter Connections and remove unwanted apps from there.
PS: Facebook scene is probably worse since you would have unknowingly authorized many Facebook apps. See my previous post to learn more.