The United States National Security Security Agency reportedly used the recently uncovered "Heartbleed" security exploit to access information, Bloomberg reports. According to two unnamed sources, the NSA exploited the flawed security standard for the past two years without alerting affected companies and the public at large. It's unclear what the exploit was used to access, but the flaw affects a huge portion of the web: something like two-thirds.
Major services like Google are already acting, updating services and patching the issue. For those services, we suggest updating your passwords ASAP. For the still affected sites? Sadly, your best option is to wait it out.
Update: The NSA insists that it only became aware of Heartbleed at the same time as everyone else. This answer isn't going to satisfy everyone given the many contradictory claims about the agency's activities, but hey -- at least it's on top of the situation.