Did The NSA Know About or Exploit Hearbleed Bug?

Kim Zetter at Wired has asked whether the National Security Administration had used the "heartbleed" bug, citing the words of Matt Blaze, a cryptographer and computer security professor at the University of Pennsylvania:

 “It would not at all surprise me if the NSA had discovered this long before the rest of us had,” Blaze says. “It’s certainly something that the NSA would find extremely useful in their arsenal.” 

Michael Riley at Bloomberg went even further:

"The U.S. National Security Agency knew for at least two years about a flaw in the way that many websites send sensitive information, now dubbed the Heartbleed bug, and regularly used it to gather critical intelligence, two people familiar with the matter said.

The NSA’s decision to keep the bug secret in pursuit of national security interests threatens to renew the rancorous debate over the role of the government’s top computer experts. . . Putting the Heartbleed bug in its arsenal, the NSA was able to obtain passwords and other basic data that are the building blocks of the sophisticated hacking operations at the core of its mission, but at a cost. Millions of ordinary users were left vulnerable to attack from other nations’ intelligence arms and criminal hackers."

 The NSA has not publicly responded to a query about whether these claims are true.