Facebook officials on Wednesday admitted to digging up dirt on Jewish billionaire George Soros and its competitors less than a week after The New York Times published an explosive exposé on the tech giant.

Elliot Schrage, Facebook’s head of communication and policy, published a blog post detailing the company’s decision to hire Definers Public Affairs, a Republican opposition research firm, and why it aimed its effort at the company’s critics, including Soros.

“Some of this work is being characterized as opposition research,” Schrage wrote. “But I believe it would be irresponsible and unprofessional for us not to understand the backgrounds and potential conflicts of interest of our critics.”

Last week, Facebook CEO Mark Zuckerberg denied having any knowledge of the company’s PR campaign against Soros until the Times investigation, which also found negative campaigns aimed at Apple and Google, was made public.

Sheryl Sandberg, the company’s chief operating officer, also denied having knowledge of the hiring of Definers. However, in a statement supplementing Schrage’s blog post, she said she recently learned that the PR company’s work had “crossed my desk.”

Facebook has since cut ties with Definers.

Schrage defended its attacks on Soros as a response to the liberal financier calling the company a “menace to society” during a speech at the World Economic Forum in Davos last January.

“We had not heard such criticism from him before and wanted to determine if he had any financial motivation,” Schrage said Wednesday.

“Later, when the ‘Freedom From Facebook’ campaign emerged as a so-called grassroots coalition, the team asked Definers to help understand the groups behind them,” he added, referencing a group partly funded by Soros, who is often the target of anti-Semitic conspiracy theories.

Definers “prepared documents and distributed these to the press to show that this was not simply a spontaneous grassroots movement,“ Schrage explained.

According to the Times investigation, Facebook initially hired Definers to monitor press coverage of the company. Facebook later expanded its relationship to include promoting negative coverage of Google and Apple, whom Facebook views as rivals.

Schrage accepted blame for not properly managing Facebook’s relationship with Definers, explaining that as its work with the PR firm expanded, the relationship was “less centrally managed.”

“Mark and Sheryl relied on me to manage this without controversy,” Schrage wrote, noting that he approved the decision to hire Definers “and similar firms.”

“I’m sorry I let you all down,” he added. “I regret my own failure here.”

But Schrage also partly blamed company culture.

“Our culture has long been to move fast and take risks. Many times we have moved too quickly, and we always learn and keep trying to do our best,” he said.

In an interview with CNN on Tuesday, Zuckerberg said he had no intention of stepping down as chairman of Facebook.

This article has been updated with comment from Elliot Schrage.