"Sadly, this particular developer certificate (assigned to a Maksim Noskov) has been used for probably two years in similar attacks," said Johannes Ullrich, dean of research of the SANS Institute's Internet Storm Center, which on Thursday publicly disclosed the campaign. "So far, it apparently hasn't been revoked by Apple."
This is a change from the previous categorization of the upgrade as an 'optional update' and it means that there is renewed potential for unwanted installations. After the launch of Windows 10, there were numerous reports of not only the automatic download of OS installation files, but also unrequested upgrades. The changed status of the update means that, on some machines, the installation of Windows 10 could start automatically.