As a young leader of Hungary's democratic movement before the fall of communism, Orban received a grant from the Hungarian-born Soros's Open Society Foundation (OSF) to study at Oxford University.
"Our relationship went bad because he went bad, he has changed a great deal," said the 87-year-old Soros in a video published on an OSF-run website.
"Back then, he was one of the leaders who helped to create democracy. But he changed and he transformed democracy into an anti-democratic regime."
Orban has created a "mafia regime," according to Soros, where "leaders used their positions to keep themselves in power and to get rich".
"The current system suppresses people more than under the Russian occupation," he said, as under communism it was easier to help people get information.
In the 1980s Soros sent photocopying machines to Hungarian civil groups to improve citizens' access to information.
The comments follow a rare statement last week by Soros that blasted "lies" contained in a months-long government campaign attacking his alleged pro-immigration stance.
The right-wing Orban has been stepping up his attacks on Soros this year calling him a "public enemy" for his "liberal agenda" and alleged encouragement and even orchestration of mass migration into Europe.
Orban, who is running for re-election next year, says the "poison" of Muslim immigration poses a security risk and threatens Europe's Christian culture and identity.
In October the government, which also says Soros is influencing EU policy, sent a "national consultation" survey to households to canvass opinion on what it calls the "Soros Plan".
The survey, which the government calls a "democratic exercise", has been accompanied by a nationwide poster and media blitz that prominently features the Jewish emigre financier's laughing face, an image that Hungary's leading Jewish organisation has said could stoke anti-Semitism.
Earlier this year parliament, dominated by Orban's ruling Fidesz party, approved a law seen as targeting non-governmental organisations supported by Soros, and another that has threatened with closure a Budapest university Soros founded after the fall of communism.
In a radio interview on Friday Orban said the recent remarks by Soros amounted to an "entry" by his "network" into the 2018 election campaign.
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