Facebook has revealed that as many as 87m people – 37m more than initially thought – may have had their data improperly shared with Cambridge Analytica.

The revelation was shared toward the end of a post from Facebook’s CTO, Mike Schroepfer, where he outlined the host of changes that would be made to the social network over the next few months to better protect user data.

“In total, we believe the Facebook information of up to 87 million people — mostly in the US — may have been improperly shared with Cambridge Analytica,” wrote Schroepfer.

Despite Facebook’s claims, Cambridge Analytica disputes the figure along with the notion that the user data is received was obtained illegally or used during the US presidential election campaign.

“Facebook reported that information for up to 87m people may have been improperly obtained by research company GSR. Cambridge Analytica licensed data for no more than 30m people from GSR, as is clearly stated in our contract with the research company. We did not receive more data than this,” said Cambridge Analytica in a statement. “We did not use any GSR data in the work we did in the 2016 US presidential election.

“Our contract with GSR stated that all data must be obtained legally, and this contract is now a matter of public record. We took legal action against GSR when we found out they had breached this contract.

“When Facebook contacted us to let us know the data had been improperly obtained, we immediately deleted the raw data from our file server, and began the process of searching for and removing any of its derivatives in our system.”

Either way, starting Monday 9 April, one of the planned changes to Facebook will see people shown a link at the top of their news feeds to see what apps they use and the information shared with the apps. As part of this, Facebook will inform people if their information may have been shared with Cambridge Analytica.

Other changes expected over the next few months include changes to the apps that are allowed access to Facebook’s Events, Groups, and Pages APIs, a tightening of the third-party Facebook login process, changes to search and account recovery – after the revelation that scammers had been taking advantage of phone number and email search functionality – and more.

Furthermore, in a separate post, Facebook outlined how it will be clearer about its terms and data policies. This includes telling users how their data is used to create a personalised experience and what information is shared with others.

Speaking to the press, Facebook CEO Mark Zuckerberg once again made it clear the company had failed its users and that he, being the founder of the social network, would take full responsibility for what has happened.

“We didn’t focus enough on preventing abuse and thinking through how people could use these tools to do harm as well,” said Zuckerberg. “That goes for fake news, foreign interference in elections, hate speech, in addition to developers and data privacy. We didn’t take a broad enough view of what our responsibility is, and that was a huge mistake. It was my mistake.”

He later added, when questioned about firing anybody over the Cambridge Analytica scandal: “At the end of the day, this is my responsibility. So, there have been a bunch of questions about that. I started this place. I run it. And I am responsible for what happens here… I still think that I’m going to do the best job to help run it going forward. I’m not looking to throw anyone else under the bus for mistakes that we’ve made here.”