This indicates an attack attempt to exploit a Security Bypass vulnerability in Adobe Reader and Acrobat.
The vulnerability is due to an error in the vulnerable software when handling race conditions. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application.
Adobe Reader XI (11.0.09) and earlier 11.x versions
Adobe Reader X (10.1.12) and earlier 10.x versions
Adobe Acrobat XI (11.0.09) and earlier 11.x versions
Adobe Acrobat X (10.1.12) and earlier 10.x versions
Security Bypass: Remote attackers can bypass security checking of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.