'...It is this latter ability that has caused so many problems for Facebook users. Third-party plugins such as "SuperWall" claim to extend functionality of the Facebook application, but have behaved in anything but a friendly manner. SuperWall would randomly send messages to existing people in a user's Facebook friends list, claiming that they had to install SuperWall in order to read a new message from that user. Once installed, it would keep performing this trick with the next person, and so forth. As it turned out, this behavior was by design.'
from Between black and white: the state of grayware on the PC