Ask HN: What does Y Combinator to prevent fraudulent use of the YC brand?

If a founder of a YC-backed company leaves and starts a new company, are YC comfortable with that founder implying their new company is a YC company when in fact they themselves were part a YC firm and not their current firm. I am asking this because a friend got really messed around by a firm that claimed to be YC backed. The use of YC branding gave him the reassurance to choose this firm over another firm. Unfortunately this firm did not deliver against its contract and my friend was put in a difficult and expensive spot. Since this is a firm that is a) trading on YC name and b) damaging the YC brand I would have thought YC lawyers would be cracking down on this type of activity. What is YC position on this?