Securities fraud class actions are big business for lawyers. Since 1996, nearly 4,000 suits have been filed, with the majority resulting in companies paying substantial settlements. The top 10 settlements alone totaled about $35 billion; plaintiffs' lawyers took home billions in fees. Companies paid their own lawyers similar sums for defending them. If spending these gigantic sums on lawyers deterred corporate fraud (that is, if they helped sort cases of actual fraud from mere business reverses), then that might be money well spent. But if lawyers are paid billions without reducing the probability or magnitude of corporate fraud, then from a social welfare perspective these payments to lawyers are a deadweight loss.
Henderson, M. Todd and Adam C. Pritchard. "From Basic to Halliburton." Regulation 37, no. 4 (2014): 20-7.