Business bites: Another credit crunch?

Fitch has downgraded its ratings of six of the world's largest banks - Bank of America, Goldman Sachs, BNP Paribas, Barclays, Deutsche Bank and Credit Suisse - citing the difficult financial and economic conditions.

But if the banks stop lending, does it mean we could face another credit crunch?

Meanwhile in the US, Zynga, the online games maker behind Mafia Wars and FarmVille, is to raise $1bn on its US stock market debut.

Zynga has 200 million users a month but only makes a revenue from 3% of them, so how does Zynga make money?

The BBC's Aaron Heslehurst discusses the key business stories of the day.