The scheme is rather clever and far-reaching. After having entered their Twitter login credentials - and effectively giving them over to the scammers - the victims are redirected to a website displaying a fake YouTube video set against a fake Facebook background.
In order to view the video, the users are urged to download an update for YouTube player:
As expected, the offered file is no software update, but the Umbra malware loader, which creates hidden files, starts executables in folders, and enslaves the machine into a botnet.
The scammy app page has already been removed by Facebook but, nevertheless, users are advised to download software updates from official sources and not to trust every private message they receive via social networks.