In a recent opinion, the Texas bar's ethics committee found that a law firm must stop representing a litigation client if it hires a lawyer who formerly worked on the case as a law clerk at the firm representing the opposing party.
Screening the tainted lawyer to prevent the sharing of any confidential information he learned in his prior employment won't enable the firm to continue representing the client.
UPDATE: 3-22-19: However, two years later, in 2016, the opinion was withdrawn and replaced with a new one which concludes "Under the Texas Disciplinary Rules of Professional Conduct, a law firm is not required to withdraw from representing a client in a lawsuit if the law firm hires a new lawyer who, before becoming a lawyer, was employed as a law clerk for the law firm representing the opposing party in the lawsuit and in that capacity helped provide services to the opposing party with respect to the lawsuit, so long as the law firm screens the new lawyer from any personal participation in the matter to prevent the new lawyer’s communicating to others in the law firm confidential information that the new lawyer and the law firm have a legal duty to protect."
You can read the new opinion here.
Under the Model Rules, a firm would be allowed to continue the representation of the current client if it screened the newly hired attorney.
