lustyd
Well-Known Member
It's a little bit technical, but they monitor traffic going to port 80 or 443 on the content server with a User Agent showing it is initiated by a web browser and a content type of web data. Email uses other ports.
MS AutoUpdate traffic as well as updating other programs will eat into the 500MB, as will Skype and most video streaming as this will all be counted as other data, based on content type and/or destination port.
The ports are not really used in this these days, it's all done by a big proxy system. A company called Byte Mobile does this (they are the ones putting the lower quality images in too where you have to press ctrl + R to improve).