The SEC is going to hang them over crap like this.
Which part, exactly?
Where to start....
Investment companies have to register marketing material. It is reviewed by the SEC to ensure that claims like "You can get 26% return on your money" don't get before the public. You'll notice any ad for a registered investment will have fine print which explains the risks of losing money. You may see historical return data but a reputable company (not that Prosper is) will NEVER speculate on what your return might actually be.
Based on what I'm reading here it sounds like Prosper is advertising an investment product, making inflated statements of potential return (specific percentages) and not fully disclosing the risk to potential investors. I highly doubt the ads are SEC reviewed.
In cases where the material is limited in use the marketing material may be reviewed by a Principal (like a series 26) but the same basic rules apply. You can't make exaggerated claims. Maybe Prosper is taking the stance that this marketing is limited? Regardless, I highly doubt that anyone at Prosper is registered to sell securities. I further doubt that there is any of the required compliance oversight. I wonder what the SEC would think about that?