Friday's high court ruling to uphold Livedoor Co. founder Takafumi Horie's prison term is significant because the judiciary has restated its zero tolerance of activities that undermine fair stock market trading, experts said.

"The ruling was no surprise, considering the scale of losses by investors and the viciousness of the defendant's acts," said Shin Ushijima of law firm Ushijima & Partners. "The high court sent a warning to authorities watching securities laws to get a grip."

The Tokyo High Court upheld the March 2007 district court-imposed 2 1/2-year prison term for the dot-com mogul for falsifying financial statements and violating the Securities and Exchange Law.