UPDATE: The New York Times said on Tuesday night that it had "terminated its relationship" with Boies Schiller Flexner. The paper's statement said in part: "We never contemplated that the law firm would contract with an intelligence firm to conduct a secret spying operation aimed at our reporting and our reporters. Such an operation is reprehensible, and the Boies firm must have known that its existence would have been material to our decision whether to continue using the firm. Whatever legalistic arguments and justifications can be made, we should have been treated better by a firm that we trusted."

In a message to lawyers and employees at his firm on Tuesday, David Boies said Harvey Weinstein is no longer a client, and that Boies "would never knowingly participate in an effort to intimidate or silence women or anyone else".

But law school ethics professors said multiple questions arise for Boies in the wake of a New Yorker report that the Boies Schiller Flexner chairman contracted with an agency linked with former Israeli Mossad agents, in a bid to stymie efforts by The New York Times to expose Weinstein's pattern of alleged sexual harassment.

"These are all serious issues. David Boies has a great reputation. I'm not going to say he crossed the line, but there are some serious issues," said Laurie Levenson, a professor of law at Loyola Law School in Los Angeles.

Top among those issues, according to Levenson: Could Boies' actions on Weinstein's behalf have deterred women from coming forward, potentially even skirting the line of suppressing witness testimony?

Levenson said The New Yorker article also raises questions about Boies' adherence to obligations to clients and former clients about confidentiality, and about potential conflicts of interest if his work for Weinstein undermined the work of the Times, which was also a Boies Schiller client.

Boies did not respond to multiple requests for comment on Tuesday. In his email to staff, Boies said his firm's engagement letter with the newspaper "made clear that we needed to be able to continue to represent clients adverse to the Times on matters unrelated to the work we were doing for the Times".

"There is a lot coming at us fast and furious here," Levenson cautioned. And she noted that a fine line separates lawyers' efforts to determine what allegations they may face on the one hand, and actual suppression of witness testimony on the other.

Almost immediately after The New Yorker story was posted, The New York Times lashed out at Boies, whose firm represented the newspaper in two pending matters and a third that has been concluded, according to a Times spokeswoman.

"We learned today that the law firm of Boies Schiller and Flexner secretly worked to stop our reporting on Harvey Weinstein at the same time as the firm's lawyers were representing us in other matters. We consider this intolerable conduct, a grave betrayal of trust, and a breach of the basic professional standards that all lawyers are required to observe. It is inexcusable and we will be pursuing appropriate remedies," the Times said late on Monday.

Levenson said the conflicts question is "attenuated", since Boies was not representing the newspaper on a matter directly related to Weinstein. But, she said: "Clearly he has a client who feels like he was playing both sides."

In his own statement on Tuesday, Boies described what he told Weinstein when he learned about the Times running a story with allegations about the movie producer's predatory behaviour towards women:

"I told Mr Weinstein at that time that neither I nor the firm would represent him in this matter, and he hired several other lawyers to represent him. I also told Mr Weinstein that the Times story could not be stopped through threats or influence; the only way that the story could be stopped was by proving it was not true.

"Mr Weinstein, together with the lawyers representing him, selected private investigators to assist him and drafted a contract. He asked me to execute the contract on his behalf. I was told at the time that the purposes of hiring the private investigators were to ascertain exactly what the actress was accusing Mr Weinstein of having done, and when, and to try to find facts that would prove the charge to be false and thereby stop the story. I did not (nor did the firm) select the investigators (at least one of which had been used by Mr Weinstein previously) or direct their work; that was done by Mr Weinstein and his other counsel."

Such a fulsome account of what Boies told a client and what that client asked raises questions about client confidentiality, Levenson said. "Has he been revealing confidential information, information he learned by helping a client on a case?" she asked.

Ronald Minkoff, a partner in Frankfurt Kurnit Klein & Selz, who leads the firm's professional responsibility group, raised a separate concern about the activities of the investigators Boies hired. He said they appeared to engage in "pretexting", or contacting people under false pretexts and identities. "It's pretty clear that is something to avoid," he said.

He suggested that Boies retained the investigators, rather than Weinstein doing so directly, to keep the information they gained under attorney-client privilege protections. Because Boies signed the contract, Minkoff said, "he was responsible for them".

"He was either not supervising them and they were off doing things they should not be doing. Or he was supervising them. Either way, he was not steering the ship the way he should have been," Minkoff said.

Deborah Rhode, who directs the Center on the Legal Profession at Stanford Law School, offered an even harsher assessment.

"What was he thinking? This is a clear violation of ethical rules and ethical norms to run opposition research on a current client," Rhode said.

Boies' statement that he did not supervise the investigators "is a mitigating factor", but not necessarily an entirely persuasive one, she said.

"You have to have known that if you are working with organisations like those, there will be ethical issues," she said.

If there's a broader lesson based on what's known so far, said Loyola's Levenson, it's that there are limits to client service.

"The biggest problem is getting sucked in by a client," she said. "You might put on blinders and take risks you wouldn't ordinarily take and not look as closely at ethical issues."