Heartbleed is one of the biggest security flaw, silently infecting thousands of web sites including Yahoo! As per reports, within OpenSSL (from v1.0.1 to v1.0.1f), this bug named as Heartbleed, can give access to 64K of memory of your server to any connected client. This bug was exposed to hackers since December 2011 and does not leave any trace on servers to let system administrators know whether security has been compromised or not.
Google Security’s Neel Mehta found this bug and reported to OpenSSL team, which had released a quick patch to fix this issue.
You can test whether your server is infected or not from this site –