No risk meaning it's not like btcjam where the borrower can just decide not to pay back. Bitfinex will liquidate your margin position before you go negative. So borrowers don't have the option of not paying back their loans.

Of course the risk exists that the operators of the service are scammers or they get hacked. But that's a much lower risk than typical bitcoin loan arrangements where the guy you loan to just decides not to pay back.

I lend on bitfinex, btw.