Evernote said that no user content and person notes were accessed, but hackers were likely able to access user names, email address and encrypted passwords.
"While our password encryption measures are robust, we are taking additional steps to ensure that your personal data remains secure," Evernote wrote on its blog.
The incident is the latest in a series of other breaches, ABC News said.
In February, Twitter announced that 250,000 accounts were compromised. Facebook and Apple were also targets of hackers, ABC news reported.