Although legal ethics rules can be counterintuitive, many ethical dilemmas can be resolved by the application of common decency and morality. One basic norm we were taught as early as kindergarten, is that when you find something that does not belong to you and you know its rightful owner, you return the property to that person.
Picture this: Somehow your opposing counsel ends up with your twelve pages of notes of a meeting you and your experts had preparing a defense for your client. Instead of returning to you your attorney work product, your opponent makes copies of your notes, shares them with co-counsel, and uses them to prepare a line of questions to impeach one of your experts at trial.
Does this seem like ethical behavior to you? I hope not. The Supreme Court of California declared this conduct unethical and disqualifed the errant lawyer and his firm in Rico v. Mitsubishi Motors Corp., Cal., No. S123808, 12/13/07.
The appropriate course of action that the plaintiff's lawyer should have taken was explained by the court:
When a lawyer who receives materials that obviously appear to be subject to an attorney-client privilege or otherwise clearly appear to be confidential and privileged and where it is reasonably apparent that the materials were provided or made available through inadvertence, the lawyer receiving such materials should refrain from examining the materials any more than is essential to ascertain if the materials are privileged, and shall immediately notify the sender that he or she possesses material that appears to be privileged. The parties may then proceed to resolve the situation by agreement or may resort to the court for guidance with the benefit of protective orders and other judicial intervention as may be justified.
Exploitive behavior of this type is a recipe for disaster. Perhaps some lawyers need to go back to kindergarten to learn that you simply don't take or use property that does not belong to you.