Yahoo will stop providing the ability to use its services using users' login information on other services, specifically with their Facebook account or Google.
In order for the registered user to access any service (e-mail, Flickr, etc.), should register with Yahoo and reserve a new username and password. The reasons given by the service are the acceleration of the entry process, the existence of a username and password for entering all its services from any device, faster support customers and easier recovery of forgotten passwords.
It remains unclear - although it is considered expected - whether the practice will be adopted by all Yahoo Inc. sites. However, the expulsion of Google and Facebook accounts starts directly from the basketball service Tourney Pick'em, with users being notified via email that they would have to sign up for Yahoo to obtain a Yahoo ID or log in with a pre-existing one - note that in 2013 it recycled user IDs that had been inactive for 12 months, had to be in their account for more than a year.
Update: Following tech.in.gr's communication with Yahoo, its representative tells us that the company is working to improve the user experience, which includes the entry process to the Yahoo Sports Tourney Pick'Em service. Currently, only users of this service are required to sign in with a Yahoo usename, but the practice will be extended to all users. By using a Yahoo username, access to all Yahoo services will be shared.
Finally, the company has not announced exactly when the option will cease to exist sign-in through Facebook and Google accounts, however in the aforementioned announcement users are assured that their data will remain accessible after creation Yahoo ID, despite the fact that in the past access was through Facebook or Google accounts.