If you have an account on Healthcare.gov, you might consider getting a new password. The internet security flaw known as Heartbleed, which left everyone's personal data on Google and Facebook open for the taking, hasn't reared its ugly head at Obamacare, but the administration is encouraging users to be proactive just in case.

A Washington Post commenter complaining that the "Heartbleed thingamajig" was no big deal posted his email and social media passwords in his rant, to prove nothing would happen if they were out in the open. Something happened. What did we learn?

Today, Bloomberg cited two anonymous sources to report that the National Security Agency has been using "Heartbleed" to "gather critical intelligence" from protected internet traffic. The NSA is denying that report. Okay. But what is Heartbleed, exactly?