There is some further information to be found here.
http://www.slyck.com/forums/viewtopic.php?f=1&t=59501The Japanese authorities are simply grabbing a few folks from each network (maybe even the same folks using multiple networks ) and making an example of them as they have done before.
The network receiving the most attention is the Share network that was the successor to Winny, a program that was inspired by WinMX , the other network they have looked over was Cabos, but like WinMx its not the focus of their attention atm, Share is their true target due to its usage pattern by Japaneses folks.