Two corpses were hung from a bridge in a Mexican border town, accompanied by a hand-lettered sign warning “scandal mongers” to keep away from social media networks that report on violence.

The bodies, of a young man and woman, bound and displaying signs of torture, were discovered Tuesday dangling from a pedestrian overpass in Nuevo Laredo.

Two Web sites that report on criminal activity and drug cartels were named and threatened.

“This will happen to all Internet busy bodies,” a sign read. Using foul slang, the poster warned, “Shape up, I am on to you.”

The slayings and the display of the threats against social media users represent another dangerous escalation in Mexico’s drug wars.

“This is against everyone who posts information about organized crime,” said Omar Rabago of the group Article 19 in Mexico, which advocates for freedom of expression. “The criminals want to shut this down. They don’t want anybody to know anything.”

Lurid Web sites depicting gruesome photographs and videos of torture sessions are popular in Mexico. Formerly fringe sites such as El Blog de Narco have become virtual clearinghouses of the day’s carnage — for the public and for police and prosecutors — as well as a kind of crude scoreboard for the cartel soldiers. The Nuevo Laredo sign referred to El Blog de Narco and Al Rojo Vivo, a site that curbed its comment section after it was threatened.

As journalists who cover crime are harassed, killed, beheaded and exiled, many news organizations in the conflict zones have virtually stopped reporting on murder and mayhem. Publishers acknowledge they are self-censoring as even the largest media owners in Mexico report frequent, credible threats — and even grenade attacks — against themselves and their employees.

More than 40 reporters have been killed in Mexico since 2004, and many more have disappeared.

Into the vacuum in Mexico comes social media, as citizen bloggers and tweeters post news, rumors and updates about military blockades, gunfights and helicopters overhead.

“It’s becoming a pattern in many cities where there is widespread violence,” said Carlos Lauria, head of the Americas program at the Committee to Protect Journalists. “The criminal gangs exert control over the press. The media stops. And in the absence of news, ordinary citizens turn to Twitter and Facebook to fill the void.”

Mexican citizens and the state are struggling with what to do about the explosion of social media as it relates to crime. Some cities use social media to act as a kind of rumor control. President Felipe Calderon frequently tweets breaking news about high-profile arrests.

Two tweeters — a math teacher and a grandmother — were arrested and jailed three weeks ago in Veracruz and charged with terrorism and sabotage for allegedly posting that local schools were under attack. Panicked parents swarmed the schools to retrieve their children, but the rumor proved false. Authorities said the false tweets caused widespread chaos and car wrecks. The two face 35 years in prison.

Their attorney, Fidel Guillermo Ordonez, said that the government’s heavy-handed response is on trial as global commentators heap scorn on authorities.

The Veracruz governor is seeking an emergency session of the state congress to change the law so the two “twitteros” can be charged with disruption of public order instead.