UnitedHealth says files with personal information that could cover a “substantial portion of people in America” may have been taken in the cyberattack earlier this year on its Change Healthcare business.

The company said Monday after markets closed that it sees no signs that doctor charts or full medical histories were released after the attack. But it may take several months of analysis before UnitedHealth can identify and notify people who were affected.

UnitedHealth did say that some screen shots containing protected health information or personally identifiable information were posted for about a week online on the dark web, which standard browsers can’t access.

The company is still monitoring the internet and dark web and said there has been no addition file publication. It has started a website to answer questions and a call center. But the company said it won’t be able to offer specifics on the impact to individual data.