If you have an Activision account, it is probably the best time to change your password to something else to secure your account. Also, it is suggested that you should unlink any payment information connected with your Activision account for a few days until Activision finds out the cause of the issue and apply a fix for it. According to the reports over 500k Activision, accounts have already hacked and the number is increasing rapidly. So all the Activision account holders are suggested to change their credentials and to be safer, unlink any accounts such as the Xbox, Battlenet, PSN, accounts from Activision for a while.
According to a report by Dextro, this massive data breach let the hackers get access to usernames and passwords of the Activision accounts and they have been publicly leaked. That credentials are now being used to access the Activision accounts and the hackers are changing the credentials preventing the actual users from accessing them. Multiple Activision users have already confirmed the data breach and advised users to to change the passwords as soon as possible.
The Activision accounts are mostly used for various gaming titles such as Call of Duty which is one of the most popular gaming titles with millions of players all over the globe. Once the hackers have access to the accounts where the payment information and other account details are stored, they can use the information for various purposes which will make this hack more than just a breach in a gaming account. This is why many tech publications recommended unlinking your payment information as well as other connected accounts from the Activision account for a while. So if you also have an account on Activision, at least regenerate your password before getting hacked.
Update: Activision has claimed that the “reports aren’t accurate.” but still they didn’t say any hack wasn’t successful. So, even if the number of hacked accounts is inaccurate, it is still recommended to change your passwords which is a good practice anyways.