In New York, the rule generally is that “privity” is necessary. That is, you may sue only your own attorney. There are exceptions, however.
One exception arises when an attorney, not hired by the plaintiff, authors an opinion letter. Another exception is cited in a US District Court case in Florida.
Gunster Yoakley http://www.gunster.com has been sued by three non-US companies which allege that the law firm damaged them by not disclosing crucial information in a debt offering. As reported in http://www.law.com on 8/17/05, when Gunster represented E.S Bankest http://www.esbankest.com plaintiffs allege that it failed non-clients.
This is interesting as an exception to the “privity” doctrine.