You may not be familiar with a service called Tor. Tor is a web service that allows users to surf the Internet, use IM, and other services while keeping themselves completely anonymous. Tor is a free and open-source that is available for Windows, Mac, Linux, and Android.
The National Police Agency in Japan is now asking ISPs to begin blocking Tor for customers if the customers are found to have abused Tor online. The push by Japanese authorities is because they're worried about an inability to tackle cyber crime enabled in part by anonymizing services such as Tor. Clearly, the indication from the NPA is that there is some guilt associated with people who heavily use Tor.
The push to curb the usage of Tor in Japan stems from a case last year where a number of death threats were posted online from compromised computers. Several arrests were made in the case, but those arrested turned out to have had nothing to do with the posted messages. Once police finally caught up with the real perpetrator of the crimes, it was discovered that he frequently used Tor to cover up his cyber crimes.
The NPA also claims that Tor makes it easier for criminals to conduct financial fraud, child abuse, and to leak confidential police information. Whether or not ISPs in Japan go along with a request to block Tor remains to be seen. Privacy advocates will likely fight the request.