Ambac and its fellow bond insurer MBIA went hard at banks, accusing them of fraudulently obtaining insurance policies on subprime-backed securities. But so far, the litigation doesn't seem to have been a smashing success for the insurers.

A lot of plaintiffs lawyers in the burgeoning litigation over mortgage-backed bonds have eschewed fraud claims, opting instead for contract allegations that don't require a showing of scienter. Robins Kaplan went for fraud--and on Friday its strategy was vindicated.

Just when we were getting used to a trickle of relatively anemic securities class action settlements tied to the mortgage meltdown, Citi managed to defy our expectations on Wednesday.

This time the target is JPMorgan, on behalf of a billionaire Russian American investor who claims the bank cost him $100 million by investing in subprime mortgage-backed securities against his wishes. The bank says the suit is meritless, but Quinn partner Richard Werder tells us his client negotiated contract language with the bank that could make a big difference in the case.