The FTC took action against D-Squared Solutions in order to stop that company's deceptive trade practices and obtained a Temporary Restraining Order. D-Squared sells software to block pop-up Windows Messenger spam, as well as software to send Windows Messenger pop-up spam and advertises these products by using, not suprisingly, Windows Messenger spam.
From the FTC:
Complaint
TRO
List of web sites operated by D-Squared and its licensees
News release
The Baltimore Sun: Court halts Web 'pop-up' advertising
MSNBC: FTC disables pop-up ad firm
Microsoft: Disabling Messenger Service in Windows XP (and 2000)