To my best knowledge, this story was broken by WeeklyStandard.com in a blog authored by Jeryl Bier.

The computer code that was stolen is called DataTables, and it is exclusively provided under a GPL v2 license which requires anyone who uses the software code to keep the copyright notice visible in the code itself. This allows the original author of the code to receive attribution for creating it.

An analysis of the code running Healthcare.gov reveals that the Obamacare development team maliciously removed the copyright notice and credit attributions from the code while copying and using the rest of the code.