WhatsApp is going after unauthorized third-party apps that are designed to work with the popular messaging system.

Users sometimes access third-party clients that offer add-ons for more customization inside of WhatsApp. Now the Facebook-owned service has issued at least one cease-and-desist order to an Android app called WhatsApp+.

On Google+, a WhatsApp+ spokesman announced that the third-party app was shutting down after warnings from WhatsApp.

"Due to the circumstances that arose, and the fact that WhatsApp Inc issued a cease and desist letter to WhatsApp+, the official WhatsApp+ community is shutting down for good and will be removed by the end of the day," reads the statement, which was posted on Wednesday.

So why is WhatsApp so miffed by this service? Well, for one, it claims that these third-party services can't be trusted with user information.

"WhatsApp Plus is an application that was not developed by WhatsApp, nor is it authorized by WhatsApp," reads a FAQ section on WhatsApp. "The developers of WhatsApp Plus have no relationship to WhatsApp, and we do not support WhatsApp Plus. Please be aware that WhatsApp Plus contains source code which WhatsApp cannot guarantee as safe and that your private information is potentially being passed to third parties without your knowledge or authorization."

It's a problem other services — like Snapchat — have run into before. Reports surfaced in mid-October that thousands of Snapchat photos were leaked via third-party Snapchat apps. So concerns about security risks aren't unwarranted at all.

As well as the action it's taking against third-party apps, WhatsApp is also temporarily banning people who use them. The bans usually last 24 hours, and once the countdown ends, users can use the application again. Some, of course, expressed frustration about the situation on social media.

Banned on #Whatsapp for 14 hours for using #WhatsappPlus....... — feeling annoyed — Avinash (@Call_me_Avi) January 21, 2015

WhatsApp confirmed to TechCrunch and others that it was indeed planning to take "aggressive action" against these kinds of unauthorized apps.