Before now Apps that requires permission from your twitter account can actually send messages in your behalf and they can also post on status on your timeline but after a series of privacy tussles twitter has review its privacy content in such a way that when you grant an App access to your account it will not be able to post or send DM for you except you also permit them to do so.
Old Apps who does not have this permission will only have access to your account but will not be permitted to post or send DM for you.

Thus there is an urgent need for you to review the apps you allow permission on your twitter handle for your privacy . .

To check and revoke APP access follow this link..

https://mobile.twitter.com/settings/applications