The group has issued a number of warnings against the KKK, such as this one last month
Anonymous said the data was “a form of resistance” against racial violence.
The KKK last year threatened to use “deadly force” against those protesting over the killing of a black youth in Ferguson, Missouri.
A list of alleged KKK members published earlier in the week appears to have been fake.
That list had incorrectly outed several US politicians as KKK members and was quickly followed by a denial from Anonymous’s official Twitter account.
‘All sorts of errors’
Thursday’s list appears to detail social media profiles of people who had joined or “liked” KKK-related groups on Facebook and Google+. Many of the profiles featured racist imagery and slogans.
Anonymous said it had collected the names over the course of the last year, using a variety of ways, from “interviewing expert sources” and “digital espionage” to obtaining publicly-available information.
The group said those on the list included official members of various KKK groups “as well as their closest associates (most are also in other extremist hate groups)”. Some were listed with their alleged aliases.
“Some members of this list are quite dangerous, sociopathic individuals. Others are not,” Anonymous added in its statement accompanying the release of the list.
Some observers were not overly impressed by the list.
Mark Pitcavage, director of the US Anti-Defamation League’s Center on Extremism,told Vice News it was “low-hanging fruit, basically public source information. For most of these people it’s not a secret that they’ve been in the Klan.”
He also said there were “all sorts of errors”, including the mis-spelling of at least one person’s name.
The release of the list came on 5 November, a significant date for members of Anonymous because it is the day that Guy Fawkes attempted to blow up the English Parliament in 1605. Guy Fawkes masks, made popular in the movie V for Vendetta, have become a symbol for the group.
The group launched its campaign, dubbed Hoods Off, after the Ku Klux Klan threatened violence against protesters – including Anonymous members – who took to the streets of Ferguson, Missouri, after a jury decided not to prosecute a white police officer who shot dead Michael Brown, a black teenager, in August 2014.
In November last year, Anonymous launched denial-of-service attacks to take down a website associated with the KKK and also took over two Twitter accounts connected to the group.
Anonymous expert Gabriella Coleman has described the outing of KKK members as a “comeback” for the hacker group, which has faced criticism for failing to control members and leaking inaccurate information.
The fact that fake data was leaked earlier will be seen as an embarrassment for the group that has become well-known for backing social justice causes.
To coincide with Guy Fawkes night, Anonymous held protests in cities around the world, including one in London where there have been at least 50 arrests.