In a situation where large deposits can't be divided into different ownership classes, protecting assets fully requires dividing them among separate institutions. Brokerage accounts have a level of protection that falls outside the FDIC. The Securities Investor Protection Corp., a nonprofit funded by its participating firms, can insure accounts up to $500,000. Protection applies only if a brokerage faces bankruptcy or insolvency. Market fluctuations and bad investments, as expected, receive no protection. -- Reported by Joe Mont in Boston.