As Twitter continues to work on improving the health and safety of its users, it's updating its app permissions, which will clarify which third-party tools can access and send direct messages on your behalf.
As explained by Twitter:
"Today, we’re changing the way that third-party apps request authorization to your Twitter account, and what they can do with that access, in order to help you make more informed choices by clarifying what apps can do when you authorize them."
Up untill now, Twitter says that any third-party app with "read/write" permission has technically been able to send direct messages on your behalf. That hasn't been entirely clear to users, so to rectify this, Twitter's changing its app permissions, and improving the language used in granting such.
"Now, only apps you authorize with “read/write and DM” permissions will be able to send DMs for you. Only a small number of apps with “read/write” permissions actually sent DMs, but if you authorized one of these apps, it is possible (but unlikely) that they sent DMs without your knowledge. That will no longer be possible as a result of this change."
Essentially, Twitter is moving to better protect more private conversations by ensuring that users are aware of what they are granting permission for when signing up to a third-party tool. The effectiveness of that measure, of course, is reliant on users actually reading the specifics at the sign-up stage, but it may help to reduce scammers and questionable operators from using people's direct messages to misrepresent them for their own gain.
Twitter says that users may soon receive requests to reauthorize apps affected by this change, so if you get a new notification, this would be why. Twitter also notes that users can check which apps they've authorized at any time, and see what each is able to do, and revoke access, within their settings - and it's definitely worth regularly reviewing this list to see which apps have which type of access.
Third-party data access has become a key focus for social apps in the wake of the Cambridge Analytica scandal, and it makes sense for Twitter to updates its permissions in this regard. The impact should be minimal, but it may also serve as a good prompt to check through which apps have access to change elements within your account.
You can read more about the changes, and how to control app access, here.