Ambrac reports loss of $6.93/share after $3.1B in subprime charges.

Ambac Financial Group Inc., the bond insurer that lost 93 percent of its stock market value in the past year, posted a wider loss than analysts estimated after $3.1 billion in charges for subprime-mortgage securities.

The world's second-largest bond insurer tumbled as much as 40 percent in New York Stock Exchange trading after reporting a first-quarter net loss of $1.66 billion, or $11.69 a share. The company's operating loss of $6.93 a share was more than three times the $1.82 estimated by six analysts surveyed by Bloomberg