The "Secret Crush" Widget suggests that someone has a secret crush on the recipient and to find out he/she has to install the Widget and oh, btw, invite five Friends to do so as well. The Widget then proceeds to install the Zango malware that we all know and love. (Remember when Zango was installed via Myspace videos?)
As I predicted in my Top Ten Threat Predictions for 2008 below these malicious uses of social networks will become yet another challenge to safe use of the Internet. Look for more to come!
Full disclosure: I work at Fortinet. Occasionally the FortiGaurd team *does* scoop the world and I will take advantage of that to get the word out here on emerging threats. Especially when I can say "I told you so!"