(Bloomberg) -- Sandvine Inc., the U.S. company whose technology helped Belarus block much of the internet during a disputed presidential election last month, promotes its wares with a stark selling point: it can be used to “blacklist” as many as 150 million websites.

The private-equity-backed technology firm demonstrated its equipment to a government security team in Belarus in May, two people with knowledge of the matter said, and its marketing materials boast of the blacklisting capabilities, according to documents reviewed by Bloomberg. The Sandvine equipment is also used to manage and secure networks, and its website blocking feature can prohibit users from accessing content deemed illicit, such as terrorist propaganda or child pornography, according to the documents.

For several days in August, however, Sandvine’s “deep packet inspection” equipment played a central role in censoring social media, news and messaging platforms used by protesters rallying against President Alexander Lukashenko’s re-election, Bloomberg reported last month. On Wednesday, White House Press Secretary Kayleigh McEnany called the Aug. 9 election “fraudulent.”

The documents and product demonstration, as recounted by the people familiar with the company’s affairs, lend added insight into Sandvine’s work in Belarus, showing that company representatives met directly with officials in Belarus and later shipped the equipment, via a contractor, to be installed at data centers in Minsk.

U.S. Senator Dick Durbin called on the Treasury Department to investigate Sandvine for potential violations of U.S. sanctions on Belarus. For more than a decade, those sanctions have imposed restrictions on U.S. companies from providing funds, goods or services that benefit Lukashenko or others engaged in “actions or policies that undermine democratic processes or institutions,” according to Erich Ferrari, a Washington-based sanctions expert.

Sandvine declined to comment. A company spokesman had previously directed a Bloomberg reporter to its corporate ethics policy, which says that a committee reviews sales to determine the risk of its products being used in a manner “detrimental to human rights.” In 2017, Sandvine was acquired by California-based private equity firm Francisco Partners in a deal worth $444 million. Francisco Partners then merged Sandvine with Procera Networks, a U.S. company. Francisco Partners didn’t respond to a request for comment.

During a Sandvine conference call on Thursday, which sought to address employee concerns about its work in Belarus, executives said they had been working with a government organization in the country for more than a year. Sandvine had provided Belarus with technology that is filtering about 40% of all internet traffic moving in and out of the country, the executives said. They said the work didn’t violate U.S. sanctions. A recording of the call was shared with Bloomberg.

Alexander Haväng, Sandvine’s chief technology officer, acknowledged during the call that Belarus may be using the company’s equipment to block websites and messaging apps, but he said that Sandvine had concluded that the internet, and access to specific material on websites, wasn’t “a part of human rights.”

“We don’t want to play world police,” he said. “We believe that each sovereign country should be allowed to set their own policy on what is allowed and what is not allowed in that country.”

The revelations about Sandvine have prompted criticisms from U.S. senators, a human-rights organization and Belarusians now living in the U.S., and it has also ignited internal protests within Sandvine, according to the two people familiar with the matter.

“It would be deeply troubling if American technology is being used by the last dictator of Europe to block Belarusians from the internet just as thousands peacefully protest a stolen election and brutal political arrests,” said Durbin, a Democrat from Illinois, in a statement to Bloomberg. “It doesn’t take much research to realize which potential autocratic clients should not have access to such technology. As such, I have asked the Treasury Department if there might be any violation of existing U.S. executive orders or sanctions with regard to this question.”

Senator Marco Rubio, a Republican from Florida, offered similar criticism.

“Reports that technology from a U.S. company is being used by the Lukashenko regime to censor and restrict citizens’ access to the internet in Belarus is troubling,” he said. “The recent sham presidential elections were marred by violence and repression against the Belarusian people and political opponents. The U.S. and the international community should stand in support with the people of Belarus in their fight for freedom and democracy.”

Belarus’s Interior Ministry didn’t respond to requests for comment.

Deep packet inspection can be used to inspect and manage internet networks, filtering out viruses and blocking hackers and prioritizing some types of traffic over others. It can also be used for eavesdropping and online censorship, according to Christopher Parsons, a senior research associate at the University of Toronto’s Citizen Lab. The rules are sometimes determined by the Internet Service Provider or the relevant network administrator, Parsons said, but often the equipment also comes equipped with predefined blacklists.

Sandvine shipped its equipment through a primary contractor, Russia-based Jet Infosystems, which finalized a technology deal with Belarus in early 2019 for $2.5 million, the documents state. Jet Infosystems didn’t respond to messages seeking comment.

The Sandvine technology has been installed at two sites in Minsk, where the National Traffic Exchange Center, a state-controlled organization, uses it to help manage the country’s internet activity, according to the documents. The National Traffic Exchange Center declined to comment.

The equipment gave the center the ability to blacklist as many as 150 million website URLs -- stopping people in the country from visiting them, according to the documents and people familiar with the matter.

The government used Sandvine’s technology to block people from accessing social media websites such as Facebook and Twitter, messaging apps such as WhatsApp and Telegram, and international news websites, Bloomberg reported last month.

On Tuesday, a group of U.S.-based Belarusian citizens wrote to Francisco Partners requesting that it “immediately withdraw and recall all supplied equipment, goods, funds or other services that were used or will be used by the Lukashenko government.” The letter, seen by Bloomberg, calls on Sandvine “to show the world that your company chooses to stand with Belarus and other nations that fight for democracy and freedom.”

Peter Micek, general counsel at the human rights group Access Now, called on federal authorities to investigate Sandvine and Francisco Partners and questioned the effectiveness of Sandvine’s business ethics committee.

“Their services appear to have been used in Belarus to silence people and to cover up egregious human rights violations,” Micek said. “The outcomes here speak for themselves. Whatever reviews they had were not sufficient and don’t give us any faith that the company takes its human rights obligations seriously.”

Pressure on Sandvine’s leadership has also mounted within the company, causing unrest among employees, some of whom didn’t know about the work in Belarus until it was revealed last month by Bloomberg, according to the two people familiar with the company’s affairs.

In the last two weeks, the people said, Sandvine employees at offices in Canada, Sweden and the U.S. have complained to their managers and circulated messages and videos discussing the situation in Belarus. The employees have questioned whether technology they helped design is aiding the Belarusian government’s crackdown on peaceful protests, which has resulted in more than 6,000 people -- including journalists and passersby -- being detained and hundreds of cases of torture and ill treatment, according to the United Nations.

During Thursday’s conference call, employees questioned asked about the company’s business in Belarus and raised concerns about damage to Sandvine’s reputation. Mark Driedger, the chief operating officer, said the company planned to keep all information about the work in-house and warned that any employees who spoke publicly about it could face termination.

“We are open to a debate internally on how to improve,” said Haväng, the chief technology officer. “Nobody really feels good about the situation in Belarus.”

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