The hacker group known as Anonymous on Thursday posted credit card numbers in retaliation for what it claimed was an FBI raid arresting one of its members.
The group said Barrett Brown was arrested in an FBI raid while participating in an online chat Wednesday.
Contacted by AFP, the FBI declined to comment.
But a video posted by the group, a loosely knit collective with no clearly defined leadership structure, showed the chat interrupted by what appeared to be a raid.
In retaliation, the group posted "these 13 credit cards details as teaser," saying they were "potentially belonging" to government officials.
A Twitter posting said the offshoot of the group, called Antisec, "retaliates on Barrett Brown arrestation."
According to a report on the website The Hacker News, Brown came to notoriety when he threatened to release the names of 75 collaborators of the Mexican Zetas cartel for kidnapping an Anonymous member.
The report also said he founded Project PM, which collects information about the intelligence industry and what it claims are threats to privacy and democratic institutions.