Next Media founder Jimmy Lai Chee-ying hit out at the "state-level" hacking that targeted him and also revealed that the hackers gained access to his photocopier, which was linked to the internet to back up the documents.
He said this was how they gained details of some donations to pan-democrats that had never been stored in his computer.
Lai said the culprits - who gained access to 900 files - had stolen his bank statements, bills, documents and email exchanges over the past 10 years on July 1, when the annual pro-democracy march took place.
The hacking activities had paralysed Next Media's server by bombarding it with 143 million cyberattacks per second and stolen all documents, Lai wrote in the latest issue of Next Magazine.
"Under [the hackers'] careful scrutiny … the worst 'scandal' exposed by them was my donations to pan-democratic parties, think tanks and some religious groups and individuals," Lai wrote.
Watch: Anti-corruption officers swooped on the Kowloon home of media mogul Jimmy Lai
"This 'scandal' is an assurance of my moral character but not a scandal."
He said the hackers had unearthed no evidence that he worked for the CIA and he dismissed such allegations as "a completely deliberate defamation".
Meanwhile, Civic Party lawmaker Claudia Mo Man-ching - who denied receiving HK$500,000 from Lai as the files suggested - branded the visit by anti-corruption officers to Lai's home yesterday as "clear-cut political persecution".
While the Independent Commission Against Corruption had not approached her, she said the watchdog's visit to Lai's residence was part of a national smear campaign against pan-democrats as the city's debate on political reform reached a climax.
"Why did [the ICAC] not take action last week or next week? The timing is suspicious," she said, with the nation's top legislature poised on Sunday to impose a restrictive framework for electing the chief executive in 2017.
Joseph Cheng Yu-shek - the convenor of the Alliance for True Democracy who jointly received HK$300,000 with Civic Party leader Alan Leong Kah-kit from Lai on behalf of the alliance - also said the ICAC had not approached him yesterday.
Democratic Party founder Martin Lee Chu-ming, a close friend of Lai, said: "I don't want to guess the ICAC's motive [behind the searches] but I know many Hong Kong people are worrying about a white terror spreading in our society."
Jimmy Lai's political donations
Labour Party lawmaker Lee Cheuk-yan: HK$1.5m (confirmed)
League of Social Democrats lawmaker Leung Kwok-hung: HK$500,000 (confirmed)
Alliance for True Democracy convenor Professor Joseph Cheng Yu-shek and Civic Party lawmaker Alan Leong Kah-kit: HK$300,000 (confirmed)
Civic Party lawmaker Claudia Mo Man-ching: HK$500,000 (denied); Democratic Party lawmaker James To Kun-sun: HK$500,000 (denied)
Civic Party ex-lawmaker Tanya Chan: HK$700,000 (denied)
Democratic Party: HK$5m; Civic Party: HK$3m (no comment)
Convenor of Hong Kong 2020 think tank Anson Chan Fang On-sang: HK$3.5m (no comment)
Hong Kong Democratic Development Network: HK$500,000 (confirmed)
Civic Education Foundation: HK$400,000 (confirmed)
Occupy Central: HK$3-3.5m (denied)
Cardinal Joseph Zen Ze-kiun: HK$6m (no comment)
Source: leaked files