Please download the latest version of PRTG Traffic Grapher from the Paessler Website.
There are two different installers for PRTG, a public download for the Freeware and Trial Editions, and another download for the Commercial Editions (which is only available for paying customers).
PRTG Traffic Grapher is an easy to use Windows software for monitoring and classifying bandwidth usage. It provides system administrators with live readings and long-term usage trends for their network devices. The most common usage is bandwidth usage monitoring, but you can also monitor many other aspects of your network like memory and CPU utilizations.