Hatem Bazian, a veteran pro-Palestinian activist in his fifties, lives with his family on a quiet street in North Berkeley, near the campus of the University of California, where he lectures. Early on the morning of May 10, 2017, as Bazian was about to drive his teen-age daughter to school, he noticed fliers on the windshields of cars parked on his block. At first, Bazian assumed that they were advertisements for a new movie or restaurant. When he looked more closely at the flier that had been left on his BMW sedan, he realized that it featured a photograph of his face, below a tagline that read, “He supports terror.” Bazian quickly folded up the flier so his daughter wouldn’t see it.

Born in Jordan to a father from the West Bank city of Nablus and a mother from Jerusalem, Bazian has long been an outspoken champion of Palestinian causes. For decades, staunch supporters of Israel have criticized Bazian’s activism. The incident with the fliers, though, was particularly unnerving, he told me. He rented his house and did not publicize the address. His opponents, he thought, must be following him. Later that day, Bazian, who describes himself as a proponent of nonviolent protest, reported what happened to the Berkeley police. He said that officers told him they could do nothing about the harassment.

Although it is unclear who left the fliers, internal documents from a private Israeli intelligence firm called Psy-Group show that, at the time of the incident, the company, and possibly other private investigators, were targeting Bazian because of his leadership role in promoting the Boycott, Divestment, Sanctions movement, known as B.D.S. Supporters of B.D.S. urge corporations, universities, and local governments to impose economic, academic, and cultural boycotts on Israel to protest its treatment of the Palestinians. Opponents say that the B.D.S. movement aims to delegitimize Israel and hobble its economy. On its Web site, the movement states that it does not advocate for or against a resolution in which Israel continues to exist.

Psy-Group’s intelligence and influence operations, which included a failed attempt in the summer of 2017 to sway a local election in central California, were detailed in a New Yorker investigation that I co-wrote earlier this month. Before it went out of business, last year, Psy-Group was part of a new wave of private-intelligence firms that recruited from the ranks of Israel’s secret services and described themselves as “private Mossads.” Psy-Group initially stood out among its rivals because it didn’t just gather intelligence; its operatives used false identities, or avatars, to covertly spread messages in an attempt to influence what people believed and how they behaved. In 2016, Psy-Group held discussions with the Trump campaign and others about conducting covert “influence” operations to benefit the candidate. Psy-Group’s founder and C.E.O., Royi Burstien, a veteran Israeli intelligence officer who established the firm in 2014, told me that his talks with the Trump campaign went nowhere. The company’s posturing, however, attracted the attention of Robert Mueller, the special counsel, who has been investigating interference in the 2016 Presidential race.

Psy-Group’s operations against B.D.S. activists on U.S. college campuses began in February, 2016, according to internal documents describing the campaign. The company raised money in New York from Jewish-American donors and pro-Israel groups, and assured them that their identities would be kept secret. Psy-Group told them that its goal was to make it appear as though the donors were not involved in any way.

The campaign, code-named Project Butterfly, initially targeted B.D.S. activists on college campuses in “a single U.S. state,” which former Psy-Group employees have told me was New York. The company said that its operatives drew up lists of individuals and organizations to target. The operatives then gathered derogatory information on them from social media and the “deep” Web, areas of the Internet that are not indexed by search engines such as Google. In some cases, Psy-Group operatives conducted on-the-ground covert human-intelligence, or HUMINT, operations against their targets. Israeli intelligence officials insist that they do not spy on Americans, a claim that is disputed by their U.S. counterparts. Israeli officials said, however, that this prohibition does not apply to private companies such as Psy-Group, which use discharged Israel Defense Forces soldiers and former members of élite intelligence units, rather than active-duty members, in operations targeting Americans.

A Psy-Group document, from 2017, outlines a campaign to investigate supporters of the pro-Palestinian Boycott, Divestment, Sanctions movement.

Project Butterfly called for Psy-Group operatives to disseminate negative information about B.D.S. activists in ways that could not be traced back to the company or its donors. The goal, according to a Psy-Group summary of the campaign, from May, 2017, was to create “a new reality in which anti-Israeli activists are exposed and forced to confront the consequences of their actions.” The campaign’s messages were designed to convince Americans that “anti-Israeli activity” equated to “terrorism,” the company told donors. A former Psy-Group employee said these so-called name-and-shame tactics were often effective at silencing individual B.D.S. activists. “They would disappear,” the employee told me, claiming that some activists appeared to become less engaged after derogatory information about them was publicized. If an activist claimed to be a pious Muslim, operatives would look for evidence that he had behaved in ways unacceptable to many observant Muslims, such as drinking alcohol or having an affair, a former employee said. B.D.S. leaders, however, seemed to recruit new activists quickly. The former employee likened Psy-Group’s campaign to the war on terrorism, saying, “It’s never-ending.”

During the period when Psy-Group mounted its anti-B.D.S. campaign, several Web sites, including the now-defunct outlawbds.com, published information on the movement’s leaders and supporters. Definitively determining who was behind the sites is difficult because Psy-Group and other organizations involved in anti-B.D.S. work used avatars and other tactics to disguise their involvement.

In an example of the deceptive practices employed by operatives involved in the campaign, an avatar who identified himself as “Alex Walker” sent an unsolicited e-mail on August 15, 2017, to an advertising-sales broker who represented several New York-based national Jewish publications. Walker claimed that a friend referred him to the broker and said that he was impressed with his services. When the broker asked for the friend’s name, Walker dodged the question. At that point, the broker, who asked not to be named, said he suspected that Walker wasn’t who he claimed to be. Walker said that he was upset about B.D.S. and wanted the broker to place advertisements promoting outlawbds.com in the New York area. Walker said that his assistant would pay the eight-hundred-dollar fee via PayPal. The broker told me that he placed the ads and took the money despite his suspicions about Walker. “In my mind, I’m not doing anything wrong,” he said.

The outlawbds.com Web site featured short profiles of B.D.S. activists, one of whom was Peter Moskowitz, a Jewish-American supporter of the movement. His profile contained misspellings, and, at one point, referred to him as “she.” But the site contained a piece of information that surprised Moskowitz: outlawbds.com had somehow uncovered his membership in a left-wing Jewish organization critical of Israeli treatment of Palestinians, even though Moskowitz had not disclosed his involvement online or to many friends.