Ragnor: DtecNet was formed by a Danish anti piracy lobby group and does work for the RIAA.
I suspect their "detection" code looks quite a lot like the code Salty posted earlier!
To be fair, that page is billed as 'helping parents'. I can see that having a quick way for non-technical parents to know if their PC is filled up with mp3 files that they don't know about (but would be legally liable for) is a valid use case. It doesn't prove anything of course - but might prompt a profitable conversation with junior downloader.