Defense Department Chief Information Officer Terry Halvorsen is clearly a big fan of Windows 10. The Pentagon is currently in the middle of a massive upgrade, planning to transition 4 million devices to the new operating system, which Halvorsen contends provides greater security, by next year.

But an industry group says Halvorsen’s enthusiastic public comments about the Microsoft operating system are improper and run afoul of federal regulations prohibiting government officials from endorsing commercial products.

The controversy stems from comments Halvorsen made during an April 8 conference call with reporters to discuss the Windows 10 transition.

During the call, Halvorsen praised what he called the “game-changing” operating system’s security features, then added: “I would tell you if you're using a computer at home and you're not on Windows 10, you're doing yourself an injustice. You ought to be moving to Windows 10.”

In addition, Halvorsen said his office was planning to issue guidance to Pentagon employees “listing what the characteristics of Windows 10 would give you if you put it in your home system.”

Halvorsen said the guidance wouldn’t be an endorsement of Windows 10 or Microsoft specifically, but would be “about as close to an endorsement as I can get of a software product.”

In an April 27 letter to Defense Secretary Ash Carter, the Software and Information Industry Association said it has “deep concerns” with Halvorsen’s remarks, which the group says constitute an unethical endorsement of a commercial product by a government official.

“Although Mr. Halvorsen declared that his remarks do not constitute a commercial endorsement, his recommendation cannot be fairly characterized as anything other than a commercial endorsement,” stated the letter, signed by SIIA’s president, Ken Wasch.

The group pointed to the DOD Joint Ethics Regulation, which bars Defense officials, in their official capacities, from endorsing nongovernment products or using their official titles “to suggest official endorsement or preferential treatment of any nonfederal entity.”

Halvorsen’s remarks and the proposed memo to employees are “unprecedented,” according to the group, which represents more than 800 companies in the software and digital content industry.

“We urge you to ensure that the department does not issue guidance about which products employees should use outside of work,” the letter stated.

David LeDuc, SIIA's senior director of public policy, he couldn’t recall another case of such a “high-profile public statement" appearing to recommend a particular product for employees’ private use.

"This is a really unusual practice, something we can't recall seeing, something we thought was inappropriate and unhelpful for the market, so we decided to weigh in and raise our concerns," he told Nextgov in a phone interview.

Nextgov has requested comment from DOD.

The group argues Halvorsen's remarks “create an unfair advantage in the marketplace” and requested Halvorsen “publicly correct” his remarks.

“His statements have already caused competitive harm, which is why it is critical that he make very clear that the DOD is not advocating for, or against, personal use of any vendor’s product,” the letter stated.

Halvorsen is far from the only Windows 10 supporter in government.

Federal CIO Tony Scott, a former Microsoft CIO, told an interviewer at an April 12 cybersecurity conference he uses the latest version of Windows on all of his personal devices.

“I love Windows 10, actually,” Scott said, after the interview brought up Microsoft’s perceived security challenges. “It's one of the most secure operating systems there is.”

On his government devices, “we're still stuck on something else,” he added, “but (I'm) working on that."