"First, Linux and Open Source software are developed and distributed (often at no cost) under a scheme called the GNU General Public License (GPL) which, some believe, is in direct contradiction to U.S. Copyright law, to the Digital Millennium Copyright Act (DMCA), and to the recent Supreme Court decision in Eldred v. Ashcroft."
Replace ", some believe," with ", SCO wants you to believe," and everything is true.
The threat to the US information technology:
"Each Open Source installation displaces or pre-empts a sale of proprietary, licensable and copyright-protected software. This means fewer jobs, less software revenue and reduced incentives for software companies to innovate. Why should a software company invest and develop exciting new capabilities when their software could end up "freed" as part of Linux under the GPL?"
SCO failed to show its "freed" part and I wonder who knows the last time SCO innovated something?
"Linux software contains thousands of lines of my company's proprietary UNIX code - for which we receive no revenue. "
The revenue part is very frustrating for SCO. They still don't understand that they have to work to get some revenue.
"When I talk about this, some people think I'm an alarmist. I have a different view - I think that this may have already happened. Open Source software and the GPL, unchecked, are an easy way for our adversaries to circumvent our software export restrictions."
Caldera had been offering such code for several years but there is no mention about it in the letter.
To sum up: SCO continues to attack to raise their stock price. They use the same rhetoric and provide no evidence.
The entire letter is present here (PDF file).
