How do criminals find and gain entry into PBXs and key systems?

Criminals can place calls and use Dual Tone Multi-Frequency (DTMF) tones to access and manipulate PBXs, Interactive Voice Response (IVRs), Automatic Call Distribution (ACDs) and other systems in order to commit theft of long distance services or compromising internal data. Some other ways criminals can gain access are by paying for maintenance port numbers and passwords or by using computerized calling programs, automatic dialers and sophisticated software to break security systems and pass codes.