This indicates an attack attempt against a Information Disclosure vulnerability in Oracle Java SE.
The vulnerability is due to a validation error in the application when handles a malicious applet. An attacker can exploit this by tricking an unsuspecting user into visiting a webpage containing a malicious Java applet and gain unauthorized access to sensitive information.
Oracle Java SE 5.0u61 and prior
Oracle Java SE 6u71 and prior
Oracle Java SE 7u51 and prior
Oracle Java SE 8
Oracle Java SE Embedded 7u51 and prior
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
Apply the most recent upgrade or patch from the vendor.