Aol has revealed that it will soon block third-party apps from accessing its aging AIM messenger service. According to reports from 9To5Mac, the internet provider has notified Adium users that the app will stop functioning on March 28th. So far, Adium is the only service to be affected, but from the look of Aol's statement it seems as though this could just be the first casualty of ye olde AIM's imminent shutdown.
The current iteration of AIM runs on the more modern TOC protocol, so third-party apps were the only way to access the older version. That system ran on an Aol platform called OSCAR, which also provided the backbone to Apple's iChat service back in the day.