Networks

Hello everyone,

I am having bandwidth issues in my network. The current internet line from the ISP is 50Mbps, but we are not getting the complete bandwidth (almost 20Mbps is lost). I have been analyzing the network past few days using PRTG and learnt that a major portion of the bandwidth is being utilized by an unknown Source IP going towards unknown destination IP using an unknown port number(none of the IP's and Port are being shown in their respective tables, just the utilized bandwidth shown; but rest of the Source IPs, Destination IPs & Port being used are shown and their bandwidth utilization as well), So I came to a conclusion that some one in my network might be using a proxy such as hotspot shield which is taking major portion of the bandwidth and where i assume the bandwidth is being leaked. Is there any means of blocking the use of hotspot shield?. I am not sure whether this is the actual problem, Or are there any other possible problems such as a bad network layout. Help needed badly as this is my final year project.

Thanks in advance :)