Their justification is that they were federally prohibited from admitting that the surveillance existed. So no, you couldn't sue them because the fed won't admit that the software exists until their pants are around their ankles.
There isn't such a justification. They can refuse to answer questions but they can't proactively lie. And if they were ordered to lie I'm not aware of anything that indemnifies them for securities fraud either.
Their justification is that they were federally prohibited from admitting that the surveillance existed. So no, you couldn't sue them because the fed won't admit that the software exists until their pants are around their ankles.