Why is facebook sending all my friends spam messages on chat?

[z z z z]

Anything being posted automatically is because you have applications enabled. Perhaps you visited one of those spam messages and now it's controlling your account and doing whatever it wants. You need to disable applications or go through and delete any applications you aren't using. One that comes to mind is "omg this girl killed herself after her dad posted this on her wall". These things are considered junk, spam, and may even contain viruses. Never click on them because it will enable an application and replicate itself for all your friends to get infected too.