This IM worm has been affecting Yahoo Messenger users, and installs a “Safety Browser” onto the desktop (hiding behind an Internet Explorer logo). This leads the user to sites which could install spyware on PC’s. Have a look at the news article and press release for more information
So – install Windows Defender to stop any malware arriving on your machines
Use Office Communicator within your company boundaries.
Don’t click on any suspicious links…. but I really don’t need to tell you that do I?…