Heartbleed is a catastrophic bug in OpenSSL: … Basically, an attacker can grab 64K of memory from a server. The attack leaves no trace, and can be done multiple times to grab a different random 64K of memory.
This has been keeping us extremely busy at my work. We have been actively running a few different scripts scanning our customer's dedicated servers and VPSs. Not only that but we are having to reissue SSL certificates for all the customers requesting it, which has just been a nightmare.