They urged the citizens of Ferguson, Mo., to confront the police in the streets. They caused the city’s web servers to crash, forcing officials to communicate by text. They posted the names and address of the county police chief’s family. And then on Thursday they released what they said was the name of the police officer who killed Michael Brown, an unarmed 18-year-old black man, on Saturday.

Members of Anonymous — the shadowy, snide international collective of hackers and online activists — have played a key role in the growing confrontation outside St. Louis over Mr. Brown’s death, goading and threatening the authorities, and calling the effort Operation Ferguson.

Operations in the collective’s decade-long history have included taking down the World Cup website to protest poverty, helping identify assailants in a rape case in Ohio, cheering on the Occupy Wall Street movement and carrying out coordinated cyberassaults on repressive foreign governments. But this one ran into trouble faster than most.

The St. Louis police said on Twitter that the name given out was wrong, and that the man was not even a police officer. Within Anonymous there was an unusual amount of dissent. In interviews, in private chat channels and on Twitter, members accused those who had initially posted details of producing faulty information and putting one another in harm’s way by openly chatting about their methods online.