Facebook said late Friday that it had suspended Strategic Communication Laboratories (SCL), along with its political data analytics firm, Cambridge Analytica, for violating its policies around data collection and retention. The companies, which ran data operations for Donald Trump’s 2016 presidential election campaign, are widely credited with helping Trump more effectively target voters on Facebook than his rival, Hillary Clinton. While the exact nature of their role remains somewhat mysterious, Facebook’s disclosure suggests that the company improperly obtained user data that could have given it an unfair advantage in reaching voters.

Facebook said it cannot determine whether or how the data in question could have been used in conjunction with election ad campaigns. Cambridge Analytica did not immediately respond to a request for comment.

In a blog post, Facebook deputy general counsel Paul Grewal laid out how SCL came into possession of the user data. In 2015, Aleksandr Kogan, a psychology professor at the University of Cambridge, created an app named “thisisyourdigitallife” that promised to predict aspects of users’ personalities. About 270,000 people downloaded it and logged in through Facebook, giving Kogan access to information about their city of residence, Facebook content they had liked, and information about their friends.

Kogan passed the data to SCL and a man named Christopher Wylie from a data harvesting firm known as Eunoia Technologies, in violation of Facebook rules that prevent app developers from giving away or selling users’ personal information. Facebook learned of the violation that year and removed his app from Facebook. It also asked Kogan and his associates to certify that they had destroyed the improperly collected data. Everyone said that they did.

“If true, this is another unacceptable violation of trust and the commitments they made.”

“Several days ago, we received reports that, contrary to the certifications we were given, not all data was deleted,” Grewal wrote. “We are moving aggressively to determine the accuracy of these claims. If true, this is another unacceptable violation of trust and the commitments they made. We are suspending SCL/Cambridge Analytica, Wylie and Kogan from Facebook, pending further information.”

The suspension is not permanent, a Facebook spokesman said. But the suspended users would need to take unspecified steps to certify that they would comply with Facebook’s terms of service.

The Trump campaign hired Cambridge Analytica in June 2016 to run its data operations. Separately, it had hired a digital marketing firm named Giles-Parscale to run its online advertising campaigns. Parscale designed the ads; Cambridge data helped Parscale to target voters. Sean Illing laid out the connection at Vox:

Kushner hired a man named Brad Parscale, a Texas-based digital expert who had worked previously for team Trump. According to Confessore and Hakim, Cambridge Analytica convinced Parscale (who has since agreed to be interviewed by the House Intelligence Committee) to “try out the firm.” The decision was reinforced by Trump’s campaign manager, Steve Bannon, who is also a former vice president of Cambridge Analytica. It’s not clear to what extent Cambridge Analytica helped (Parscale denied that Cambridge was of any use in a recent 60 Minutes interview), but we do know that Trump’s digital operation was shockingly effective. Samuel Woolley, who heads the Computational Propaganda project at Oxford’s Internet Institute, found that a disproportionate amount of pro-Trump messaging was spread via automated bots and anti-Hillary propaganda. Trump’s bots, they reported at the time of the election, outnumbered Clinton’s five to one.

Cambridge Analytica released a statement, saying it deleted all of its data after learning that Global Science Research did not comply with Facebook’s TOS, that it is working with the social media company to “resolve this matter as quickly as possible.”

Updated, March 17th 2018, 10:30AM ET: Updated with Cambridge Analytica’s statement.