The online note-taking service Evernote is requiring all its estimated 50 million users worldwide to reset their passwords after the company's servers were hacked on Saturday 2 March.
In a statement on the Evernote blog, the company said: "Evernote's Operations & Security team has discovered and blocked suspicious activity on the Evernote network that appears to have been a coordinated attempt to access secure areas of the Evernote Service.
"As a precaution to protect your data, we have decided to implement a password reset."
The company says that it has found "no evidence that any of the content ... was accessed, changed or lost. We also have no evidence that any payment information for Evernote Premium or Evernote Business customers was accessed.
"The investigation has shown, however, that the individual(s) responsible were able to gain access to Evernote user information, which includes usernames, email addresses associated with Evernote accounts and encrypted passwords."
Evernote is a popular Cloud-based service that allows users to make notes, store videos, articles and other digital content, and then access the data - or share it with friends - on any mobile device or computer.
Evernote is the latest prominent online service to be the target of hackers.
Despite the security breach, Evernote has reassured its users: "While our password encryption measures are robust, we are taking additional steps to ensure that your personal data remains secure. This means that, in an abundance of caution, we are requiring all users to reset their Evernote account passwords."