Hackers broke into thousands of Dropbox Inc accounts last month, viewing and downloading material users kept on the cloud-storage platform, according to a company statement and records seen by Bloomberg News.

About 5,000 Dropbox accounts were compromised by the hackers, who accessed files on less than a third of them, spokesperson Tim Rathschmidt said in an email. When Dropbox learned of the issue, it moved to secure the accounts, he said, adding that the company has since notified regulators and affected users.

Shares of Dropbox fell as much as 6.6 percent in postmarket trading on Tuesday.

Some Dropbox users received an email from the company on Monday saying there was unauthorized access to their accounts between Aug 4 and Aug 21, according to notification emails seen by Bloomberg. The company told some users their files were viewed and downloaded during that time, while others were told there was no evidence of this, the emails show.

The compromised accounts weren’t protected by multifactor authentication, Rathschmidt said. 

Dropbox doesn’t expect the breaches to have a material impact on its business, Rathschmidt said.