Japan Inc. has been fingered in a mob scandal that has exposed a link between big business and organized crime. The police say the former loan sharks and extortionists have branched out beyond their traditional underworld businesses into such endeavors as funding business startups and white collar crimes like insider trading.

According to crime writer and former reporter at Japan's top-selling Yomiuri daily Jake Adelstein, "Insider trading has become huge -- you can make much more money manipulating stocks" than extorting businesses. Jake Adelstein's bestselling memoir "Tokyo Vice" is set to become a Hollywood movie. Adelstein compares the Yamaguchi-gumi, the biggest organized crime group in Japan, to "Goldman Sachs with guns".

Adelstein says Japan's modern gangsters would not look out of place in any corporate boardroom. The says the mobsters have chucked off their tough guy persona for tailored suits. Adelstein said explains "They're savvy investors. They like to gamble."

Traditionally the yakuza have made their money from such schemes as gambling, drugs, prostitution, loan sharking, protection rackets like the Chinese triads or the Italian mafia. The yakuza also run illegal ventures through front companies. Japanese authorities have looked the other way as yakuza have opened offices in major cities, only occasionally going after the criminals.

Toshihiko Kubo, professor of financial law at Ritsumeikan University said "It is baffling that Mizuho board members failed to act. Once they learned that loan recipients were related to the mob, they should have taken immediate action."

An anti-yakuza campaigner in Tokyo who did not want to be identified said "Crime syndicates...are out to make money, and they'll use whatever means available," said the campaigner, who asked not to be identified. Many companies are trying not to deal with organized crime...But It's difficult to filter everything because their methods are also becoming sophisticated."

According to police data, crackdown efforts look like they are working. Membership in yakuza dropped 28 percent to 63,000 in 2012 from a ten years ago.

Adelstein says "There are lots of politicians that, in some sense, owe their positions to yakuza support back in old days, so clearly their influence is not non-existent. It's still a bizarre system because Japan's organised crime groups are legal entities. They are regulated but not banned."