MidiDef32.exe is a Trojan.Piebot-A. MidiDef32.exe opens a back door on IRC channels. MidiDef32.exe tries to terminate antiviral programs installed on a user computer. Related files: %System%\MidiDef32.exe More info: http://www.sophos.com/virusinfo/analyses... Removal: Kill MidiDef32.exe process and remove MidiDef32.exe from Windows startup using antivirus (also check How To Remove section)Startup Optimizer.