Speaking of Refco, what exactly does SIPC protect?

SIPC may not be applicable to Refco, but while we're on the topic, what does SIPC protect? Retail securities accounts only? 125k protection? 125k in free balances? What exactly?

And who backs it up? Other flimsy securities houses? A government agency (not the same as the full faith and credit of the U.S. government), or the U.S. government?

 

Try this:

http://www.sipc.org/