Outcome Health, Chicago’s most valuable tech company, reportedly misled advertisers by manipulating data and inflating the performance of ads, according to a story in the Wall Street Journal.

Outcome employees provided inflated data to advertisers and “manipulated third-party analyses showing the effectiveness of the ads,” the WSJ found based on accounts from former employees and several advertisers.

The altered data helped increase business for the Chicago tech company, the WSJ reported.

Outcome, which installs video screens in doctors’ offices and charges pharmaceutical companies to run ads, has hired a law firm “to review allegations about certain employees’ conduct that have been raised internally,” Outcome lawyer Lanny Davis told the WSJ. Davis was the former special counsel to President Bill Clinton.

A letter posted to the Outcome website from CEO Rishi Shah stated, in part: “Integrity is the foundational value at Outcome Health—that has always been our commitment. Shradha and I, alongside our entire leadership team, have been building a company that operates appropriately, delivers effectively for our customers and continuously strives towards excellence in all of our operations.

“We have taken many actions to elevate the standards of reporting and transparency in our nascent industry…”

Three Outcome employees have been put on paid leave, the WSJ said, including Chief Growth Officer Ashik Desai.

“We are proud of the company we and our employees have built,” Outcome co-founders Rishi Shah and Shradha Agarwal wrote in an email to the WSJ. “Of course, we have had growing pains as we scaled from 4,000 to 40,000 doctors’ offices—every high-growth company does. That is why we have taken many steps to implement best practices.”

In May, Outcome raised more than $500 million from investors such as Goldman Sachs and Alphabet’s growth equity investment fund CapitalG, making it the most valuable tech “unicorn” in Chicago at more than $5 billion. Last month it announced plans for a new downtown office tower for 2,000 additional employees the company plans to add by 2022.

The same week Outcome announced the new building and hiring plans, the company held a round of layoffs. The WSJ said those layoffs totaled 76 employees.