Well Facebook has been talking up its new messaging system, but I think their are still huge vulnerabilities with the Facebook message system I have seen several examples of people spamming this messaging system. The latest example is from a friend on my Facebook sending out un solicited messages and this spam seems to link up and re send the message to even more people. I will admit one of my personal computers were hit with DR Malware software which I was un able to remove with megabytes and also via safe mode due to the fact the malware had spread over my system files so I had to re install windows and wipe every thing. This just increases the need for Facebook to increase security for users to stop this type of stuff happening.
(live example of this spam on Facebook, I have removed user names)