This indicates an attack attempt against an Information Disclosure vulnerability in OpenSSL.
The vulnerability is due to insufficient input validation in the application when handling a crafted SSL Heartbeat request. A remote attacker can exploit this to gain unauthorized access to sensitive information via the crafted SSL request.
OpenSSL 1.01 and 1.02
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
Apply the most recent upgrade or patch from the vendor.