Mandiant is pushing back against a claim in David Sanger's new book that its researched was partly aided by 'hacking back' into Chinese government systems.

Exploitation "would be incredibly difficult to pull off," the developers wrote.

Agencies like the FBI, Secret Service and NSA have limited visibility into programs that are not developed or somehow customized internally for use by White House staff.

Journalists sometimes need to work under a veil of anonymity, and in the 21st century, that often means visiting websites without anyone knowing that a major investigation…