But the company won't say how the passwords are stored, which may indicate if they can be unscrambled by an attacker.
Opera has confirmed that a hacker breached one of the company's sync servers, potentially exposing passwords.
The Norway-based internet browser maker said
in a blog post that it "quickly blocked" an attack on its systems earlier this week, but admitted that some data was compromised, including "some of our sync users' passwords and account information," such as login names.
But the company said it doesn't know the full scope of what was compromised.
Opera said that it has reset all the Opera sync account passwords as a precaution.
