An internet video - which claims to be linked to the Anonymous hacking movement - has threatened to expose details about a Mexican drugs cartel.
The YouTube message said it was "tired of the criminal group the Zetas, which is dedicated to kidnapping, stealing and extortion".
It said the cartel "made a great mistake" carrying out an abduction of one of their members in Veracruz.
Local law authorities said they cannot authenticate the video.
The message shows a person dressed in a Guy Fawkes mask associated with Anonymous and other activist groups.
The voiceover, which is in Spanish, claims to know about police officers, journalists, taxi drivers and others who aid the cartel.
It said it will publish photographs and other details unless the kidnapped member of its group - who has not been identified - is released.
"We cannot defend ourselves with weapons, but we can with their cars, houses and bars," the message added.
"It's not difficult. We know who they are and where they are."
The video was posted under the username MrAnonymousguyfawkes. It was uploaded on 6 October, but was first reported at the end of last week by the global intelligence think tank Stratfor.
An attempt to contact the video's author did not receive a reply.
Analysts at Stratfor said that if Anonymous carried out its threat, it would likely lead to the murder of those named as cartel associates by rival gangs. It said there could also be reprisal attacks against suspected hackers.
Veracruz is about 260 miles (420km) east of Mexico city, on the Gulf of Mexico.
Over recent months local authorities have reported a rise in drug-related crime. They said rivals of the Zetas cartel were challenging it for control of the area.
Drugs gangs have been linked to the killings of other campaigners who used the internet to denounce the cartels' activities.
In September the bodies of a man and woman were found hanging from a bridge in the northern city of Nuevo Laredo.
Attached signs read: "This is going to happen to all of those posting funny things on the internet" and listed the names of two blogs.
"The internet offers a space for people to challenge the cartels with some anonymity," said Robert Munks, a Latin America expert at the defence analysts IHS Jane's.
"But the cartels have exceptionally good reach and can unmask some of these internet posters, and as we've seen the consequence can be pretty dire. I think there will be further postings, and I regret, further deaths."