They include reports and research documents from the Open Society Foundations (OSF), which offers grants for humanitarian organisations, human rights groups, development projects and policy reform.
The refugee crisis and migration are among the diverse issues covered, alongside the Ukraine conflict, racial discrimination in the US, anti-corruption initiatives and education in Pakistan.
Excerpts relating to Israel and the Palestinian territories provoked a particularly strong reaction, with far-right activists calling Mr Soros “anti-Israel”.
The Jerusalem Post reported that almost $10 million had been awarded to pro-Palestinian groups since 2001 through the OSF’s Arab Regional Office, citing a 2015 document hailing “successes in challenging Israel’s racist and anti-democratic policies in the international arena”.
The Republican Jewish Coalition said the figures amounted to “undermining Israel”, while Jeremy K Nolt, a volunteer for Donald Trump’s campaign in Arizona called Mr Soros a “terrorist”.
But anti-Semites also took the leaks as proof of their conspiracy theories related to supposed plots regarding the refugee crisis and Muslim migrants.
The source for the assertion was leaked OSF reports on the refugee crisis and immigration, which has seen Mr Soros call for increased co-operation in Europe.
The Hungarian-American business magnate and philanthropist has drawn ire for decades because of his wealth and funding of liberal causes.
The billionaire, who was born to a Jewish family in Budapest and was forced into hiding during the Nazi occupation of Hungary, has long been the subject of conspiracy theories dubbed “anti-Sorosism”.
The group that published the leaked documents online described themselves as “American hacktivists who respect and appreciate freedom of speech, human rights and government of the people”.
Intelligence sources told Bloomberg the hack was believed to originate from Russia and could be the same group that accessed 20,000 Democratic Party internal emails in June.
That cache was published by WikiLeaks, with Julian Assange saying at the time there was “no proof whatsoever” of Russian state backing.
Vladimir Putin has previously dismissed similar allegations and the Russian government-owned Sputnik news website claimed American policies were “scrambling to distract from disturbing revelations”.
An email put online by WikiLeaks last week showed Mr Soros had advised Hillary Clinton on how to handle unrest in Albania in 2011, when she was Secretary of State.
On its website, the OSF says its aim is to “build vibrant and tolerant societies…with respect for human rights, minorities, and a diversity of opinions”.
Among the groups supported by the OSF is the International Consortium for Investigative Journalists, which headed the release of the Panama Papers earlier this year.
A spokesperson for the OSF told The Independent the intrusion was detected in June and was reported to the FBI, with an internal investigation finding hackers had used an intranet system used by board members, staff and foundation members.
"The materials reflect big-picture strategies over several years from within the Open Society Foundations network, which supports human rights and the rule of law in more than 100 countries around the world," she added.