Now, as someone who lives in Japan, let me say that this kind of activity [sharking] is illegal here. Japan does have indecency laws and some of them are quite strict by American standards.
It was only until recently, that Japanese adult magazines were legally able to show pubic hair. It used to be that all images of genitalia and the pubic area (including pubic hair) had to be scratched out or covered up in some kind of way. Adult videos still are not allowed to show certain sexual acts and body parts and these have to be digitally altered so that can't be clearly seen.
Of course, companies are always will to see how much they can get away with even if they know what they are doing is illegal. It is impossible for the authorities to stop all this junk from being made and distributed so some of it does get out and alot get made for overseas markets where the indecency laws allow such material. [Add] Oversea as in Western countries. ALL Asian countries pornography is illegal to market. Where I live the law is somewhat contradicting (for the better): pr0n is illegal to sell but legal to own. I can buy pr0n video in America and mail order them to me. It is also legal to distribute but to a friend only. Sharking videos are not classified as pr0n and since the juicy contents are pixelated and the videos are not copyrighted, they are therefore legal. Hence the reason why I am willing to share with you guys.
Japanese websites are the same way. There's lots of restrictions placed on what they can and can't do in Japan. So, many of these adult orientated sites use servers based overseas where the laws are less strict and not regulated by Japanese law.
Recently there has been a slight change in attitudes and this kind of behavior is becoming more and more unacceptable. And, due to overseas pressure, particulary regarding child pornography, new laws have been passed and penalties on existing laws strengthened. [Add] If the Japanese filenames are correct and real, child pornography still exist in WinMX...and very common.
Activities like sharking are crimes in Japan. There is lots of legalized adult entertainment in Japan, but sharking, prostitution, public nudity, groping, sexual assault, etc., etc are not some of them. Not only are they illegal but they are also considered morally unacceptable by most Japanese.
Some of Japanese indecency laws might seem a little vague and their enforcement arbitrary, but there are laws on the books.