Windows 10: Free Upgrade from Pirated Versions, but...

At the beginning of the year, Microsoft announced that for the first year of Windows 10's release, owners of Windows 7, 8, and 8.1 would be able to upgrade to the new operating system at no cost. It was initially implied that even owners of pirated versions would be able to take advantage of this offer. However, a few days ago, Terry Myerson somewhat retracted this belief in a blog post.
Who is Terry Myerson

Terry Myerson was born in 1972 (or 1973) and is the Executive Vice President of Operating Systems at Microsoft. He started working at Microsoft on various internet and business projects, including Site Server, BizTalk Server, and Windows Management Instrumentation. He then led the Microsoft Exchange team for 8 years starting in 2001. In 2008, he became the head of mobile engineering and in 2011 was promoted to head of Windows Phone development. Finally, in 2013, he took on the role of Executive Vice President of Operating Systems, and The Verge described him as the most important person at Microsoft.
Myerson's "but"

In a recent post, Myerson stated that contrary to what had been implied, if someone has "cracked" Windows, they will still be upgraded to Windows 10, but will see messages prompting them to purchase genuine Windows.
These messages are already appearing for users with pirated operating systems.
What Myerson does not clarify is whether this applies only to "cracked" installations or also to "clean" ISOs that were later tampered with.
The reason given for this decision by Myerson was security. As he rightly pointed out, non-genuine Windows may have undergone various modifications, which could potentially be malicious. If someone has Windows from an OEM, this security issue does not arise.