Mangham used a vulnerability to download Facebook's source code, arguably the company's most valued and secret intellectual property.

Mangham portrayed himself as a security researcher who continued to probe Facebook because he wanted to look deeper for other security issues, since most systems have "a tough outer shell and a soft inside." He wrote that in the past he had been paid by Yahoo for finding vulnerabilities.

He said he took steps to prevent damage to Facebook's systems, hard-coding a delay in scripts he used to extract the source code to prevent "throttling of the server and impeding its availability."

After he knew Facebook was on his trail, Mangham wrote he "panicked because I knew how bad it looked without sufficient context." He maintained that "almost nobody" knew he had a copy of the site's source code, and that he kept it "physically detached from the internet."

"In many respects, it was better secured than the original," Mangham wrote.