Quant hedge fund Two Sigma Investments said it put a researcher on leave after the employee tampered with the $60 billion firm’s models, which resulted in losses for some clients.

“One of our researchers engaged in intentional misconduct by circumventing our modeling practices,” the firm wrote in a letter to investors Friday. Preliminary results from Two Sigma’s review suggest the actions led to “gains to some client portfolios and losses to others.”

A representative for the New York-based firm declined to comment.

The firm said it’s still assessing the impact of the misconduct. “If we conclude that a fund experienced losses as a result of this misconduct, we are prepared to remediate appropriately,” the firm said in the letter.

It also said the incident didn’t affect the accuracy of investor account statements, and that it’s not expected to interfere with the firm’s normal operations.

“We take this matter extremely seriously and are reviewing this incident to determine what changes should be made to prevent similar misconduct,” the firm said in the letter.

The news marks the latest potential disruption for Two Sigma investors. Earlier this year, the firm said a falling-out between its billionaire co-founders had become so strained that it qualified as a material risk.

John Overdeck and David Siegel, who founded the firm in 2001, disagreed over Two Sigma’s organization and succession plans, according to a March 31 regulatory filing. The tensions were already affecting the ability of employees to fully implement key research, engineering or business initiatives, according to the filing.

This article was provided by Bloomberg News.