Yahoo! is sending notifications to its users saying that hackers may have illegally gained access to their accounts.

The notification says that a vulnerability was exploited by hackers. By manipulation of cookie files, they have managed to get an access to accounts without using a password. The mentioned attacks happened in 2015 and 2016, but only now Yahoo! decided to talk about it openly. As a result of hackers’ activity accounts of tens of millions users may be affected. Stolen user data from this new breach involves names, email addresses, telephone numbers, dates of birth, and hashed passwords.

The company believes that there is a connection between this assault and the one that was reported in last September. Then they admitted that company was hacked in the end of 2014 and at least 500 million user accounts were stolen.

Yet everything pales in comparison with to 2013 incident, when hackers stole more than one billion account records. Yahoo! wasn’t fast to react and admitted this security breach only few months ago, December 2016. In all cases, Yahoo! notified potentially affected users, and asked them to change their passwords and invalidate affected security questions.

To be on a safe side make sure you maintain the security of your own computer or refer to London IT services to remove viruses from your device.