Bad news for users of Opera's Web sync service.

The browser maker on Friday warned that hackers recently gained access to the sync system, and may have stolen users' passwords and login names. The company "quickly blocked" the attack after discovering it early last week, and has reset all sync account passwords, Opera's Tarquin Wilton-Jones wrote in a post on the company's security blog.

Opera's sync system lets you easily synchronize browsing data, including bookmarks and tabs, across multiple devices. Some 1.7 million people — or less than 0.5 percent of Opera's 350 million users — use the sync feature.

Opera reset users' passwords "as a precaution" — all synchronized passwords for third-party sites stored in the breached system are encrypted, and passwords used to access the platform itself are further protected with a technique called hashing and salting.

Still, out of "an abundance of caution," Opera is advising users to not only change the password for their sync account, but also reset any passwords to third-party sites they may have synchronized with the service. If you don't use the sync feature, you don't need to take any actions.

"We take your data security very seriously, and want to sincerely apologize for the inconvenience this might have caused," Wilton-Jones wrote.

All Opera sync users should have already received an email about the incident. If you use the feature, be sure to visit Opera's password resetting page to obtain a new password.

This article originally appeared on PCMag.com.