qmgr0.dat file is dangerous file that belongs to PC Defender virus. Be sure that you should never leave this file running in your system because it can be used for a long list of dangerous activities. As soon as it is installed on the system, it is used for launching a virus, updating it or downloading other malicious components on the computer system. Please, remove PC Defender as soon as it starts showing its fake pop-up ads that are typically used for tricking people into purchasing fake licensed version.
Remember, while relatively harmless pests may use qmgr0.dat to degrade system performance, display commercial advertisements or perform other annoying actions, really dangerous parasites may use this file for system's damage and similar malicious activities. That's why you should remove this file from the system as soon as possible. For checking the trustworthiness of this file we recommend using RegCure Pro.
Please note that the qmgr0.dat can also be a fully legitimate file that belongs to harmless application. That's why you should always double check it before eliminating it from the system.