Most mortgage-backed securities will likely remain unscathed by the destruction of Hurricane Katrina since most pools have limited concentration of affected mortgages. But bondholders aren’t guaranteed to be totally off the hook. Credit Suisse First Boston reports that 1.1 percent and 2.5 percent of all agency adjustable- and fixed-rate securities and 0.7 percent of outstanding non-agency prime and Alt A and subprime securities have some exposure. The firm estimates the highest concentration of affected agency…