The website made the files public on Sunday night. The documents, from 2007, include interrogation summaries on more than 700 detainees and describe whether government officials thought the detainee would be a threat to the United States if released.
They also reveal that Guantanamo officials named Pakistan's main intelligence agency a terrorist organization. The agency, which denies any ongoing ties to Islamist militants, declined to comment on the leak.
The disclosures, called the Detainee Assessment Briefs or DABs, are likely to provide human rights activists with additional ammunition that some cases against inmates appear to be based on flawed evidence.
However, the DABs show certain inmates were more dangerous than previously known to the public and could complicate efforts by the U.S. to transfer detainees out of the controversial prison that President Barack Obama has failed to close.
The government called the release "unfortunate."
The Associated Press contributed to this story.