Yahoo started again sent out letters to users of their services with the notice that may have fallen victim to data theft. These emails that transmit users of social media, and subsequently leading Internet media, communicate to consumers that may have been victims of theft in 2015 or 2016. The company stated that government hackers were able to steal the source code of the software to help generate cookies, thanks to which they have conducted attack on registrations of consumers through "falsification of cookies" (cookie forgery), in which attack they could reaching mailboxes and accounts of users without having to know the passwords for them. Cookies are code that helps users save time in filling the information Authorised them the site they visit. The server behind the site generates a unique code that preserves and can recognize each user, providing access to registration. It is assumed that the source in his hands, the attacking party has obtained access to the mechanism by which cookies are generated and managed to enter the boxes to consumers without their need to know their passwords. "The investigation identifies user accounts, which we believe was used stolen or forged cookies. Yahoo's in the process of notifying all affected parties, "confirmed to ZDNet representative of the company.